Pitot-Static Systems Fire Protection vs Ozone Protection Airmanship - Discipline Point of No Return - CAA
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July / August 2003
Pointing to Safer Aviation
Pitot-Static Systems
Fire Protection vs Ozone Protection
Airmanship – Discipline
Point of No Return
CONTENTS
Managing Editor, Cliff Jenks
Page 3 Pitot-Static Systems
Vector Editors, Barnaby Hill, Jim Rankin, Pam Collings,
Peter MacDonald. This article looks at how a pitot-static system
CAA News Editors, Peter Singleton, Phillip Barclay. works, what can go wrong with it, how to interpret
Design, Gusto Design & Print Ltd. erroneous instrument readings and what corrective
actions to take should a system blockage or
Published by, Civil Aviation Authority of New Zealand,
P O Box 31-441, Lower Hutt, NEW ZEALAND.
malfunction occur.
Telephone +64–4–560 9400, Fax +64–4–569 2024,
Managing Editor email: jenksc@caa.govt.nz,
CAA News Editor email: singletonp@caa.govt.nz.
Published six times a year, in the last week of every
odd month. Page 8 Airmanship – Discipline
Publication Content This article continues the series on airmanship and
The views expressed in Vector (with the exception of looks at the importance of discipline, ie, doing what
“Occurrence Briefs”) are those of the Editor or the
you know you should do.
named contributor. They are intended to stimulate
discussion and do not necessarily reflect the policy of
the Civil Aviation Authority. Nothing in Vector is to be
taken as overriding any New Zealand Civil Aviation
legislation, or any instructions issued or endorsed by
the Civil Aviation Authority of New Zealand.
Reader comments and contributions are welcome and
will normally be published, but the Editor reserves the Page 9 Fire Protection vs Ozone
right to edit or abridge them, and not to publish those Protection – What’s Happening
that are judged not to contribute constructively
towards safer aviation. Reader contributions and
with Fire Extinguishers?
correspondence regarding the content of Vector Replacement fire extinguishers with comparable
should be addressed to: Vector Editor, PO Box 31-441,
characteristics to those of halon-type extinguishers
Lower Hutt.
are not readily available. Find out how this affects
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Page 7 Nyloc Undercarriage Nuts
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Page 13 Flight Plan Overdues Update
Change of Address
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Cover Photo: A British Aerospace Jetstream Series 3200 operated by Air National Corporate Limited,
2 July / August 2003 on the western apron at Wellington International Airport.
Aircraft pitot-static systems are relatively simple and effective most of the time. They can, however, become blocked
by foreign objects and provide erroneous pressure instrument readings, which could have disastrous consequences
for the unwary pilot. This article looks at how the pitot-static system works, what can go wrong with it, how to interpret
erroneous instrument readings and what corrective actions to take should a system blockage or malfunction occur.
I
t is possible that many more accidents lists (the pilots of the Boeing failed to can be extremely hazardous in instru-
and incidents are caused by pitot- follow the pre-takeoff checklist and ment meteorological conditions, as the
static system blockages and mal- turned the pitot heat switch OFF); pilot may unwittingly descend below the
functions than is able to be determined don’t trust instruments that indicate minimum safe altitude for the route. If a
through investigation. Some pilots appear performance beyond the capability of blockage does occur the pilot has two
to be unaware of the dangers associated the aircraft (at one point the Boeing’s options:
with such blockages/malfunctions, and instruments indicated a continuous 5000 • Switch to the alternate static cabin-air
their effect on pressure instrument fpm climb at an IAS of 340 knots); make source. If the aircraft is unpressurised,
indications. This is of concern, as the sure you understand how the pressure the ambient pressure inside the cabin
winter months bring the highest instruments work; and be aware of the will be similar to the pressure outside.
likelihood of pitot-static blockages from pitot-static blockage symptoms. There will be a degree of inaccuracy
ice. A lack of knowledge in this regard in altimeter and VSI readings as cabin
The following sections deal with
could have fatal consequences. pressure varies with airspeed, attitude
understanding problems that can occur
Many years ago, a Boeing 727 on a flight in the pitot-static system and the and the positioning of the ventilation
from New York to Buffalo entered a spin appropriate actions to be undertaken to controls. When the vents are open,
as it climbed through 24,800 feet. It avoid a malfunction developing into an the air rushing in tends to pressurise
crashed 83 seconds later, (the average in-flight safety issue. the cabin. This increased pressure is
descent rate was 17,000 fpm) killing sensed by the altimeter as a lower
everyone on board. The flight data altitude. The altimeter will conse-
recorder showed that the pilots were Altimeter and Vertical quently under-read, but this is a safer
deceived by erroneous airspeed indic- Speed Indicator alternative than having the vents
ations caused by an ice blockage in the closed and having the altimeter over-
pitot-static system. The airspeed had Blocked Static Sources reading. It is, therefore, advisable to
increased steadily during the climb, If all static sources become completely open the cabin vents when using the
which encouraged them to raise the blocked, the vertical speed indicator alternate static source during an
nose further to reduce the airspeed. This (VSI) will read zero regardless of whether instrument approach.
process continued until the aircraft’s the aircraft is climbing or descending. • If no alternate static source is available,
attitude was nearly 30º nose-up before it The altimeter will record the elevation the glass on the face of the VSI should
stalled and entered a spin. that the blockage occurred at and will be broken (unpressurised aircraft).
This accident highlights some important not change, regardless of changes in This allows cabin air to flow slowly
factors: always follow appropriate check- altitude. Totally blocked static sources Continued over ...
VECTOR July / August 2003 3
... continued from previous page
into the instrument and through the drome where a visual approach can be Blocked Static Sources
static lines to the altimeter and carried out. A complete blockage in the static system
airspeed indicator (there will be a can affect the ASI even if the pitot head
noticeable lag in the ASI and altimeter Airspeed Indicator is clear. If the aircraft is in level flight
readings). When breaking the glass of there will be no indication of a
the VSI, care should be taken not to Pitot Blockages and Leaks malfunction and the ASI will read
damage the pointer. (Be aware that the The most common reason for the pitot normally. If the static sources become
VSI will now give reverse readings.) head becoming blocked is ice. If this blocked during the climb, the static
occurs on the ground in an aircraft pressure surrounding the diaphragm
Partially Blocked Static Sources with independently located static vents, remains constant, stopping the expansion
Static sources are also prone to partial the ASI will register zero on the takeoff of the diaphragm as altitude is gained.
blockages from bugs, dirt and blowing roll. If the aircraft is then climbed, The ASI will under-read as a conse-
sand. Partial blockages can also occur if a the unaffected static air pressure quence. During the descent, the static
pilot flies an aircraft after recent rain or surrounding the diaphragm decreases, pressure will not increase and the
after it has been washed. Water droplets allowing the diaphragm to expand. This diaphragm expands more than it should,
and/or condensation in the static lines causes the indicated airspeed to increase
resulting in the ASI over-reading. This is
can freeze when climbing to altitudes progressively as altitude is gained, even
potentially very serious because the pilot
above the freezing level. though the true airspeed of the aircraft
will believe that the aircraft is going
Partial blockages are very dangerous may remain constant. If the aircraft is
faster than it actually is. The aircraft
because their symptoms vary according then descended without pitot pressure,
will be closer to its stalling speed, the
to the degree of blockage and can be the static pressure increases and com-
potential consequences of which need
difficult to interpret. If a partial blockage presses the diaphragm resulting in a
little elaboration.
occurs with the aircraft in level flight, progressive decrease in indicated airspeed
and it is then placed into a climb, the as altitude is lost.
Partially Blocked Static
altimeter and VSI will lag (respond after If there is a leak in the pitot head line Sources
the aircraft starts the climb) and indicate then the ASI will simply under-read in
less than true values. The symptoms of a partially blocked static
all situations.
source are slightly different to those of a
If the aircraft then flies straight and level, To prevent icing, the pitot heat must be complete blockage. If the blockage occurs
the instruments will slowly catch up and used at all times when flying in visible in level flight the ASI will read normally.
read correctly. If the aircraft descends, moisture. (Note that in a light piston-
the altimeter will over-read and the VSI If the blockage occurs during the climb,
engine twin, the reduction in engine
will indicate a slower rate of descent power caused by selecting pitot heat ON the system static pressure will reduce at a
than actual. This could result in the prior to takeoff could be critical to slower rate that normal, slowing the
pilot believing that the situation is safer single-engine performance following expansion of the diaphragm as altitude is
than it really is. It is recommended that an engine failure after takeoff.) The gained. The ASI will therefore show a
the alternate static source be activated operation of the pitot heat should be slight under-read. If the aircraft is then
at least once when on approach in checked before every flight as part of the leveled from the climb, the ASI will
instrument meteorological conditions. preflight checks. Turn on the pitot heat continue to under-read until the static
If the instrument pointers change and immediately check the pitot head by pressure slowly equalises, whereupon it
significantly after its activation, a static touching it to feel if it is warm. The pitot will read normally.
problem exists and the alternate source heat should not be left on for long During the descent, the static pressure
should be used for the remainder of the periods of time when the aircraft is on will increase at a slower rate than normal
approach. Consideration should then be the ground, as the heater relies on air and the diaphragm expand more than it
given to initiating a missed approach and moving past it to prevent overheating should, resulting in the ASI over-reading
diverting to a suitable alternate aero- and burning out the element. slightly. If the aircraft is then leveled from
To Pressure Instrument
To ASI Static Lines Static Vent Heating Element
Diaphragm
Pitot
Pressure
Heater Element Cable Static
Pitot Tube Drain Hole
External Drain Holes Pressure
Figure 1. – Basic Pitot-Static Pressure Head
4 July / August 2003 VECTOR
descent, the ASI will continue to over-
read until the static pressure equalises, Pitot-Static System – The Basics
whereupon it will read normally. The pitot-static system is a simple system of tubes used to transmit dynamic and
static pressures from the points at which they are sensed on the aircraft to the
Drain Holes pressure instruments.
For the pitot-static system to work Figure 2 is a simplified diagram of a pitot-static system typical of most general
effectively there needs to be a method of aviation aircraft. Static pressure (the pressure of the localised atmosphere) is
eliminating water that enters the system. transmitted to all three pressure instruments. This pressure is taken through static
This is achieved through the provision of vents located on the side of the fuselage or a pitot-static head underneath the
drain holes in the pitot head and drain wing. The altimeter measures the change in the surrounding pressure like a
valves in the system pipelines. Usually barometer, except that the change in pressure is calibrated to be read as an
these drain holes are very small so they altitude. For example, when the aircraft climbs, the static pressure reduces and this
do not introduce any instrument error (see reduction is registered as an increase in altitude.The vertical speed indicator (VSI)
figure 1). If the main pitot head becomes measures the rate of climb or descent by sensing the rate of change in the static
blocked but the drain holes remain clear, pressure as the aircraft climbs or descends.
then static pressure can still enter through
the pitot tube drain holes, and this pressure Main Static Line Figure 2. –
will be exactly equal to the static pressure VSI ALT ASI Typical
surrounding the diaphragm. This results in 5
10 15
9
0
1
180
AIRSPEED
KNOTS
40
Pitot-Static
the ASI reading zero. 0
System
UP VERTICAL SPEED 60
8 2
0 20 ALT
1030
1035
160
100 FEET/MIN 80
DN 7 3
5 140
6 100
4
System Serviceability
15 120
Normal 10 5
Static Source
Pitot Line
Checks Alternate Static Source
The serviceability of the pressure instru-
ments and the associated pitot-static
system should be confirmed during the Dynamic +
preflight and monitored during flight. Pitot Head Static Pressure =
Pitot Pressure
Before flight, ensure that the pitot and
static sources are clear of contaminants, Left Static Source Right Static Source
the pitot cover is removed, and the pitot
head is securely attached and free of
damage. The operation of the pitot heat Figure 3 is a simplified diagram of the airspeed indicator (ASI) system. The ASI
(if fitted) should be checked, as indicated measures the speed of an aircraft relative to the surrounding air, using the
previously. The pressure instrument differential between the pressure of still air (static pressure) and that of moving air
faceplates should be checked to ensure compressed by the aircraft’s forward motion (ram pressure). Ram air plus static
that the glass is secure and free of cracks. pressure entering the pitot head result in a pitot (total) pressure, which is
The ASI should read zero and the transmitted through a pipeline to a sealed diaphragm inside the ASI. The static
altimeter should be accurate to within pressure component of pitot pressure in the diaphragm is balanced by the
plus 30 feet and minus 45 feet of the surrounding static pressure (taken from the static vents) inside the instrument
correct altitude. The VSI should read casing. The amount of expansion or contraction of the diaphragm, and therefore
zero, but is considered serviceable if the the movement of the needle, is proportional to the change in dynamic pressure.
needle shows no more than plus or
minus 200 fpm. ASI (Side View) Pitot Pressure
Figure 3. –
In flight, the pilot should ensure that the
Instrument Face
To Diaphragm ASI Pitot-Static
ASI needle comes off the stop shortly Linkage
after the start of the takeoff roll and, and IAS
System
Static
Pointer Pressure
once airborne, that the VSI indicates a
climb rate that approximates that
stipulated in the Flight Manual for the To Electrical Source
given conditions. En route, the pitot heat Alternate Static Source
should be used continuously if there is
visible moisture present. If flying within
radar coverage, a check of indicated Normal Static Source Heating Elements
altitude versus the altitude provided Mast Pitot Pressure
(Dynamic Ram
by ATC can be done. Periodically, the Air Pressure
pilot (particularly if on an instrument Plus Static
Pressure)
approach) should activate the alternate
static source to confirm that there is not Left Right Drain Hole
Pitot Head
Static Source Static Source
a significant difference between the two
pressure readings. Continued over ...
VECTOR July / August 2003 5
... continued from previous page
If any discrepancies occur then the pilot ASI
should continue to use the alternative
Climb Level Flight Descent
static source.
Leaking Under-read Under-read Under-read
A summary of pressure instrument errors
Increasing airspeed with Reads the speed at which Decreasing airspeed
associated with various types of pitot- Pitot Head Blocked
increasing altitude the blockage occurred with decreasing altitude
static system blockages/malfunctions is
Partial Blockage Under-read Under-read Under-read
provided in the accompanying tables as a
Leaking Over-read Over-read Over-read
quick reference.
Static Source Blocked Under-read No change Over-read
Summary Partial Blockage Under-read Lag then normal Over-read
It is recommended that all pilots, VSI
especially pilots of IFR aircraft, become
Climb Level Flight Descent
and remain familiar with how their
aircraft’s pitot-static system works. Leaking No change No change No change
Learning what can go wrong with it, Static Source Blocked Zero Zero Zero
how to check its serviceability, how to Partial Blockage Under-read Lag then normal Under-read
interpret erroneous instrument readings
and what corrective actions to take Altimeter
should a system blockage or malfunction Climb Level Flight Descent
occur is important. This is definitely
Leaking Over-read Over-read Over-read
preferable to waiting until an in-flight
Static Source Blocked Reads the altitude of the blockage and will not change
pitot-static problem is experienced and
possibly learning the hard way. Partial Blockage Under-read Lag then normal Over-read
Faulty Seat Belt Inertia Reels
T he recent failure of a seat belt inertia reel mechanism fitted
to a Piper Arrow has highlighted an underlying design fault
in some models of inertia reel that are commonly used in
Pacific Scientific Inertia Reel
New Zealand aircraft. Recoil spring
retainer cover
The fault relates to Pacific Scientific inertia reels manufactured
before June 1992 whose part numbers fall within a range
specified by the manufacturer. (The manufacturer issued a
Service Bulletin, Pacific Scientific SB A 25-1124A in June
2000, to specifically address this issue.)
The problem is being caused by the hardened steel seat belt
guide bracket wearing through the central aluminium alloy
retention shaft (see photographs for details). In some cases the Severed central aluminium
alloy retention shaft
retention shaft has been completely severed, which normally
causes the reel to jam, but could result in it pulling loose from
its mounting. Reels manufactured after June 1992 contain a
stainless steel retention shaft, which corrected the problem.
If you own or operate an aircraft that has Pacific Scientific
inertia reels fitted, check that they do not fall into the specified
range (refer to the above Service Bulletin for details). If they
do, have your maintenance provider rectify the problem –
preferably by replacing the reels. One reported indicator of
the problem is a fine aluminium dust mark on the seat
belt webbing near the reel, but this is not always visible.
Unfortunately, the retention shaft is not visible without dis-
mantling the reel.
We urge you to take the time to ascertain whether or not your
aircraft falls into this category, and to take corrective follow-up
action if it does. The alternative is perhaps having a faulty
restraint system that fails when it is most needed, something Hardened steel guide bracket
that does not bear thinking about.
6 July / August 2003 VECTORSeat Belt Standards
V ector has received a letter from an LAME “Seat belts are the Inspections. In addition to some general
employed with an airline. He enclosed a inspection criteria listed, seats and safety belts
photograph of the seat belt in an aircraft in last line of defence are required to be inspected for “poor condition,
which his son, who is learning to fly, had been – and we expect apparent defects, and security of adjustment
offered a flight. devices”.
“As you can see, the alloy buckle has a huge scab
them to perform As with most maintenance, how well these
of corrosion and the steel tongue is badly rusted when it matters.” criteria are judged and acted upon depends on
[see accompanying photograph]. If this was in a the professional integrity, skill and knowledge of
car, it would not get a warrant of fitness, so what’s it doing in an the licensed engineer carrying out the inspection.
aircraft?
The inspection would include such things as:
“Seat belts in a crash are the last line of defence for the
occupants – maybe they are taken too lightly by some people. • Examining each strap for wear, damage, broken stitches,
discolouration and deterioration.
“I informed the pilot that I did not consider the seat belt safe
and he assured me that he would have it rectified.” • Examining attachments and fittings for security, wear and
The poor condition of this seat belt is certainly cause for elongation of attachment holes.
concern. • Checking the release mechanism and means of adjustment
Civil Aviation Rules, Part 43 General Maintenance Rules outlines for freedom from slip.
in Appendix C the procedures for Annual and 100-hour
• Checking the action of the release mechanism.
• Checking each inertia reel for correct function and freedom
of operation.
There are extensive standards that must be met in the
manufacture and continuing service of aircraft restraint systems
(which is reflected in rule 91. A.4 Restraints) and any inspection
is aimed at ensuring that the belts continue to meet those
standards.
Aircraft owners have a key responsibility – an engineer may
only see a private aircraft once a year.The ultimate responsibility
for ensuring the aircraft is maintained in an airworthy condition
lies with the owner.
Seat belts are the last line of defence – and we expect them to
perform when it matters. It is a relatively small price to pay to
ensure they are kept up to scratch – infinitely preferable to a
hospital or funeral bill.
Nyloc Undercarriage Nuts
In the “GA Defect Incidents” section of the last issue of Their application is usually associated with high-
Vector we reported on a Piper PA-28-161 landing gear bolt temperature environments, but best practice suggests that
shearing. The defect rectification action stated was: “New they will hold their torque more effectively than the
bolts and Nyloc nuts have since been fitted to the Nyloc version no matter where they are used. This may
undercarriage assembly and the area closely monitored at be the reason why metal nuts are specified for PA-28-161
each inspection”. undercarriage bolts and may explain why the reported
Thank you to an eagle-eyed reader (Frank Higham) who problem occurred in the first place. In any event, the
noted that the reference to Nyloc nuts was incorrect. The correct replacement nut is not the Nyloc version.
PA-28-161 Parts Catalogue refers to the nut in question as It is also interesting to note that an Internet search on the
Part Number MS20365-428C. However, reference to the subject unearthed two Service Bulletins warning of the
parent Military Standard MS20365 shows that the suffix use of Nyloc nuts where the metal version has been
‘C’ is for nuts fabricated entirely from metal. specified.
VECTOR July / August 2003 7Airmanship – Discipline
Previous articles in this series have discussed a model of airmanship that can be described by using the catch-phrase
‘Detect – Determine – Decide – Discipline – Do’. This article considers the fourth aspect of the model, Discipline.
Discipline drivers in a lot of countries the
road rules appear non-existent.
What do we mean by the term
The standard of driving is truly
‘discipline’? In the opening article
unbelievable to us, but because
of this series it was described in
everyone does it, it is the accepted
terms of ‘doing what you know you
norm. Changing such attitudes
should do’. At first glance this seems
takes time. It wasn’t too long ago
like a ridiculous statement – doesn’t
that drink-driving was socially
everybody do what he or she knows
acceptable in New Zealand. That
they should? Unfortunately, no!
culture is fortunately changing for
The first article also asked the
the better. Aviation has its own
rhetorical question about how
problems with safety culture, though
many readers had ever exceeded
once again attitudes do seem to be
the speed limit while driving.
changing, mostly for the better.
Almost all of us will admit to
having done so, and can come up A pilot’s level of discipline is
with a host of reasons to excuse therefore strongly influenced by the
what we did. Deep down we know cultural environment, but the pilot’s own
we shouldn’t speed, but somehow we attitudes have an equally important part to play. Researchers
often end up doing so. In our model such behaviour would be have determined that there are five ‘hazardous attitudes’ that
characterised as a lack of discipline on our part. are most commonly exhibited by pilots who display poor
discipline.
There are many examples of similar sorts of behaviour in
aviation; either things we do, or often, things we don’t do that
we know we should. The following is a list of some of the The Hazardous Attitudes
more common examples of poor discipline that experienced • Anti Authority – Some people don’t like being told what
instructors often see: to do, and out of spite will often do the opposite. This can
• Failure to adequately prepare for flights, check NOTAMs, quickly lead to breaking rules, limits or exceeding whatever
get up-to-date weather, etc. the pilot has been authorised to do.
• Poor or rushed preflight inspections. • Impulsiveness – This means to act without thinking,
• Carrying out-of-date publications and maps. considering or analysing the situation.
• Failure to adequately brief passengers about the flight. • Invulnerability – It can’t happen to me. Sorry, it can!
• Inconsistent checks, or sometimes no checks at all! • Machismo – Some people like to take unnecessary risks,
• Inaccurate flying through laziness. maybe for the adrenaline rush, or perhaps out of a mistaken
belief that they need to prove themselves or impress others.
• Failure to keep accurate, tidy and complete logs for
navigation flights. • Resignation – The feeling that trying again or trying
harder is not going to solve the problem, so not even
Ever done any of these things? If you are like most pilots, and bothering to do anything about it.
are honest, then the answer is likely to be yes. The next
question is “Why?” Have you ever recognised any of these symptoms in yourself? If
so, the chances are that your level of flying discipline is not
what it should be.
The Causes of Poor Discipline
The degree of discipline that an individual pilot applies to his
or her flying is closely related to the attitudes they have towards
The Solution to Maintaining
flying and safety. This in turn can be strongly influenced by the Discipline
culture that pervades the environment that they operate in. There is a very simple strategy that you can use to improve
An organisation with a strong safety culture is likely to breed your level of discipline – pretend that every flight you do is a
well-disciplined pilots. An organisation with a lax culture will check flight with an ASL examiner. It is pretty well guaranteed
unfortunately engender a lack of discipline in the individuals that you won’t deliberately do anything stupid on such a flight.
within it. You will be on your best behaviour. You will be very unlikely
To take a non-aviation example, how many of you have had to display any of the hazardous attitudes listed above.
the experience of driving in some third world countries? If If you can do it with an examiner on board, then you can do it
you have, then you are likely to be well aware that for most on all your flights.
8 July / August 2003 VECTORPhotograph provided courtesy of Glenn Williams, ‘Wormald’.
Fire Protection
vs
Ozone Protection
– What’s Happening with Fire Extinguishers? –
T Maintenance Checks
he March/April 2002 edition of CAA News ran an
article regarding the withdrawal of halons, or BCFs (bro
mochlorofluoromethane), as fire extinguishing agents in Weighing Problems
accordance with the 1987 Montreal Protocol, which aimed to It has been found that many extinguishers in light aircraft pass
reduce damage to the ozone layer. The article proposed that
the weight test, but in fact have no propellant pressure
dry powder was the safe alternative to halons. There are, how-
remaining. The nitrogen propellant may leak out over time, due
ever, some associated problems with the use of dry powder
to the ‘O’ ring neck seal in the cylinders perishing, as they only
extinguishers and we will discuss these, and other alternatives,
have a design life of 18 to 20 years. Weighing is therefore of
in this article.
limited value, as it is only possible to ascertain the weight of the
The majority of fire extinguishers fitted to aircraft in the past liquid halogen, or dry powder in the cylinder. Without the
have been of the halon type. They are light, small, and provide
nitrogen charge the effective operation of the extinguisher can-
the best ‘knockdown’ effect on fires.
not be assured in an emergency. Some imported extinguishers
As the last of the halon stocks are being used up, it is timely to are fitted with pressure gauges and although scarce, these types
have a look at the alternatives. The problem is that replacement are the preferred option.
fire extinguishers with comparable characteristics to the halon
types are not readily available. Hydrostatic Check
The CAA Rules A hydrostatic check of the cylinder is required every five years.
This involves a pressure check, which measures the percentage
Civil Aviation Rules, rule 91.523 Emergency Equipment
of permanent expansion of the cylinder when it is subjected to
requires that aircraft used for commercial operations, capable
a specific pressure loading.
of carrying one or more passengers, have a readily-accessible
portable fire extinguisher. The number of extinguishers When a cylinder is charged, the pressure causes expansion, or
required is in accordance with an accompanying table, eg, stretch, of the metal. When the pressure is released, the cylinder
passenger numbers of one through thirty require one handheld will contract back towards its original dimensions. When
fire extinguisher. recharged, it will expand again. Over time, this expansion and
Civil Aviation Advisory Circular 43-6 Emergency Equipment contraction will weaken the cylinder. The purpose of the
requires that: “…each portable fire extinguisher should be hydrostatic check is to ensure that the cylinder hasn’t expanded
weighed at intervals not exceeding 12 months. The weight beyond a certain specified point. If it has, it must be discarded.
shall not be less than that specified by the manufacturer for a The process requires that the extinguishing agent and the
fully charged extinguisher.” propellant first be removed from the cylinder. Continued over ...
VECTOR July / August 2003 9... continued from previous page
As it is now illegal to release halons to the atmosphere, most New Products
portable extinguishers containing halons are being treated as A new extinguishing agent has been developed in the United
storage vessels, which have a 12-year life. They must then be States that has similar properties to halon, but is more ozone-
disposed of in an approved manner. As Halon 1211 (most layer friendly. This product, called halotron, is probably not yet
portable fire extinguishers contain this derivative of halon) has available in New Zealand as this would depend on someone
not been manufactured since 1987, extinguishers being classed making a substantial investment in a service facility, for a
as storage vessels have now exceeded this 12-year life. limited market demand. Halotron is expensive – a new
Although there are still limited stocks of halon left in extinguisher of this type costs around NZ $1000. Halotron
New Zealand, these are mainly supplied where expensive fixed units manufactured in the USA have an Ozone Depletion
systems are used, such as in engine compartment installations Potential (ODP) of 0.014 compared to halon units, which have
on larger commercial and military aircraft. an ODP of 1.0.
Carbon Dioxide Extinguishers
At the moment the only practical
alternative to halon is carbon
dioxide. This can be used on
Class A, B and C fires. Class A
fires involve solid materials such
as wood, cloth, paper, rubber and
many plastics. Class B fires
involve flammable liquids or
grease, and Class C fires are
electrical.
The ‘knockdown’ effect of
carbon dioxide is not as good as
halon or dry powder, mainly
because it does not have the
cooling properties of the other
British Aerospace Jetsteam Series 3200 engine compartment fire protection system. chemicals. It relies on a flooding
factor, reducing the oxygen
Significantly larger quantities of carbon
Approved Extinguishing Agents concentration to between 14 dioxide extinguishing agent are
percent and 10 percent. Oxygen required to put a fire out than is the
Rule 91.523 currently approves the following extinguishing case with halons.
concentrations of less than 14.8
agents for fire extinguishers: percent will not support flaming combustion in the majority of
• Halon 1211. cases. Significantly larger quantities of the carbon dioxide
• Halon 1301. extinguishing agent are required to put out a fire than is the
• Carbon dioxide. case with halons.
• Dry Powder; or The carbon dioxide extinguisher should be held one to two
• Another agent which provides an equivalent extinguishing metres from the base of the fire and gradually moved forward
action. and upward, the nozzle swinging in slow, even arcs.
Security of Extinguishers cockpit, such as the Pitts Special, consideration should be
given to having the latch secured. To this end, the military,
in the Cockpit and some civilian installations, use soft copper annealed
In order to be readily accessible and secure in flight, fire wire to secure latches. This is easily broken when required
extinguishers should be fastened in the aircraft with an in an emergency, while retaining security of latches from
approved quick-release bracket. Installation is a job for a inadvertent unlatching.
licensed aircraft maintenance engineer.
An unsecured fire extinguisher, which could weigh as
much as three kilograms, would be a hazard flying around
the cabin during turbulence, or rolling around the floor.
Using a bracket to mount it makes its exact location certain
in an emergency.
There have been instances where a fire extinguisher latch
has been inadvertently released when pilots enter or exit
the aircraft, presenting the hazards referred to in the above
paragraph. There have been incidents where the
extinguisher has been expelled through the rear cabin
window of a Cessna 152 Aerobat. In order to prevent this It has been known for the extinguisher to be expelled through the rear cabin
from happening, particularly in aircraft with a confined window during aerobatics or in turbulence.
10 July / August 2003 VECTORRapid motion, or advancing too quickly, can leave areas highly corrosive to aluminium and other metals and to
where the fire appears to be out, only to rekindle because of wash it off as quickly as possible. This we did, and treated
surrounding hot temperatures. the whole engine bay with corrosion inhibitor. My concern
is that had we not been informed of this, we would
Dry Powder Extinguishers probably have blown as much of
the powder out as possible with an
Dry powder extinguishers have a
air gun, and any residual would
good ‘knockdown’ capability, and
probably have been left to disperse
are effective on Class A, B and C
in its own time, as it obviously
fires. They do, however, have some
doesn’t pose a fire hazard. An
associated problems – the powder
operator who has an inadvertent
may cause respiratory and visibility activation inside the cabin would
problems in confined spaces. The probably have done much less,
Fire Service has stated, however, perhaps only vacuuming up the
that if the dry powder extinguisher residual powder, thereby posing a
is utilised properly by a trained significant hazard to the aircraft,
person, a very small discharge of Training in the proper use of dry powder fire extinguishers in confined particularly since it could be up to
spaces is essential.
extinguishing agent can be used in a 12 months until its next inspection.”
confined space to better effect than
a carbon dioxide extinguisher and with minimal risk of Conclusion
incapacitating a person. It is therefore considered that a small
Light aircraft and helicopters used for commercial and charter
aircraft cockpit fire could be contained effectively using a dry operations have a need for a suitable portable fire extinguisher
powder fire extinguisher with minimal risk to the occupants replacement to the halon types that have been in use for many
provided it was used properly. Training in its proper use in years.
confined spaces is therefore essential.
From all of the above information it would appear that, as yet
When operating a dry powder or a carbon dioxide fire
there is no really good substitute for halon (or BCF) type
extinguisher, it is important not to panic and release all of the
portable fire extinguishers available in New Zealand. However,
contents in one go. In other words – don’t blow it all at once! here is a summary of the preferred options based on the
With carbon dioxide, the fire might rekindle and you wouldn’t information we have:
have any extinguishing agent left to put it
out. • Existing halon fire extinguishers that are
fitted with a pressure gauge are still the
If you release all of the charge in a dry
preferred option, however, these may be
powder extinguisher within the confines of
hard to obtain.
the cockpit, you will likely have breathing
and visibility problems. The powder re- • The next preferred option is carbon di-
leased, which is finer than talcum powder, oxide.
will persist in the atmosphere for some time • Dry powder is next, provided training in its
before dissipating. use has been given and that there is an
awareness of its associated limitations and
Corrosive Effects of Dry Powder problems.
The optimum would be the new ozone-
The chemicals used in dry powder
friendly product, halotron, which has been
extinguishers are corrosive to aluminium
developed in the USA, but availability is
and other aircraft components. In a life-
uncertain and it is comparatively very expen-
threatening situation, the extinguisher
sive.
should always be used, as the detrimental
effects of the fire would almost certainly We recommend that operators arrange fire
be greater than the consequences of As yet, in New Zealand, there is no really extinguisher training for their pilots and other
good substitution available for halon (BCF)
discharging the extinguisher. Nevertheless, type portable fire extinguishers. operational staff. The companies involved with
after a dry powder fire extinguisher has fire protection systems, or the Fire Service,
been discharged, the corrosion issue needs to be addressed and may be able to assist with this – ask at your local Fire Station,
appropriate remedial maintenance action taken. or Airport Rescue Fire Unit.
The following account was received from the principal of an
aircraft maintenance engineering facility: Footnote The Australian Civil Aviation Authority (CASA) has approved Halon BCF
units made as special batches by Chubbs in Australia. These could be made available,
“We recently had an incident where a dry powder subject to an import licence here and an export licence in Australia. Any imports, however,
would need the support of a service facility. Presently, Air New Zealand will only service
extinguisher was discharged onto an aircraft, and it has units with a specific aircraft part number, and these Australian units would probably not
brought to light some issues regarding the types of have this. We are aware that the Chief Operating Officer of one fire protection system
company is presently involved in discussions with the Ministry for the Environment and the
extinguishers that are able to be used on aircraft. Ministry for Economic Development, as well as the New Zealand Civil Aviation Authority,
with a view to investigating the viability of importing some of these units into New Zealand.
The extinguisher used was a dry powder type (mono-
ammonium phosphate), and upon talking to a fire Acknowledgments: We thank John Fraser, of ‘Halon Recycling N.Z. Ltd,’ for his assistance in
extinguisher service centre, we were informed that it was providing valuable information during the preparation of this article.
VECTOR July / August 2003 11Point of No Return
Some Fatal Mistakes alarm would have been raised as soon as their SARTIME was
exceeded and Search and Rescue personnel would have had
The aircraft was on a VFR flight from the West Coast of the
some idea of where to start looking.
South Island to Twizel in the Mackenzie Basin. The weather
was fine on departure from the West Coast, but it appears that What is PNR?
no pre-flight weather information was obtained by the two
The lesson this article addresses is the concept of point of no
pilots or flight plan filed. On reaching the Mackenzie Basin
return (PNR). This is the point on a flight beyond which the
they found themselves caught VFR on top of a low cloud layer,
aircraft has insufficient fuel to get back to the departure point.
with insufficient fuel to return to the West Coast. They were
A cardinal rule of aviation is that pilots should never go past
apparently trying to reach Alexandra when the fuel ran out.
PNR unless they can be assured that weather conditions at
The aircraft crashed onto mountainous terrain near the Lindis
their destination (or a safe alternate aerodrome) will allow for a
Pass and was probably in cloud at the time of impact. The
safe arrival.
accident was fatal.
You may think the PNR is something that applies only to
It is sobering to consider what must have been going through
bigger aircraft on long flights, particularly oceanic crossings,
the pilots’ minds when they realised their predicament; caught
and indeed it is an extremely important flight-planning factor
in VMC on top over mountainous terrain and running out of
for such flights. (The author of this article spent many years
fuel. It must have been even worse when the engine finally
flying Hercules to Antarctica. On these flights, the PNR back
quit and they had nowhere to go but down into the cloud.
to New Zealand was normally at around 65 degrees south. This
was about the start of the ice pack with some 1000 NM, or
What Can We Learn? three hours flight time, still to go to McMurdo. If the weather
We can learn a number of lessons from this accident, including changed for the worse during those three hours life could get
the necessity of obtaining thorough pre-flight weather very interesting.)
information and the importance of filing a flight plan. While But, PNR also applies to VFR flights around New Zealand.
filing a flight plan probably wouldn’t have made much There are significant areas of the country where aerodromes
difference to the pilots’ chances of survival in this instance, it or suitable landing areas are few and far between, particularly
certainly would have if they had survived the impact. The on the West Coast, in Fiordland and the mountains of the
PNR Calculation • PNR is always earlier if there is any wind – either
PNR can be calculated before flight using the following headwind or tailwind on either leg. In the above example,
formula: the nil-wind PNR is at 125 NM. Conversely if the wind
X = POH / O+H, where increases to 50 knots, PNR decreases to 93.75 NM.
X is the distance from origin to PNR, • This formula only works for straight out-and-back
flights, where the wind stays the same and your cruise
P is the safe endurance (fuel burn at cruise power with a
airspeed and fuel consumption are the same on both the
specified reserve),
outbound and homeward legs.
O is the planned groundspeed out from the origin to
destination, and O
H is the planned groundspeed you would have for the H
return trip.
PNR = 120 NM
Consider a flight from A to B 200 NM apart. Your aircraft A B
cruises at 100 knots. For the trip out there a tailwind of 20 200 NM
knots is planned for, so O = 120 and H = 80.You have a safe
endurance of 2.5 hours (plus a reserve). Therefore: 20 knots
X = 2.5 x 120 x 80 / 120 + 80 which equals 120 NM.
If you fly past this point, you won’t have sufficient fuel to get
back without eating into your reserve.
Try putting some other numbers into this equation, or
O = 120 knots
calculate PNR for flights you might undertake. Some points
to note are:
• To keep units consistent, if you calculate speed in knots,
and distances in nautical miles, then your endurance must H = 80 knots
be expressed in decimal time as in the above example.
12 July / August 2003 VECTORSouth Island. Even the North Island ranges, especially inland of any changes to wind en route, that could change the PNR. In a
Gisborne, can pose just as much of a problem. Rapid changes number of circumstances, particularly when you have other
in weather conditions, especially when crossing mountain suitable alternate aerodromes to divert to, an out-and-back
ranges, can also leave pilots in similar situations to the one PNR may not be the best way of approaching the problem.
faced by the pilots in this accident. Instead, you must have calculated the amount of fuel you need
to reach the designated alternate. At any time in flight you must
How is PNR Applied? always have an aerodrome, or other safe landing area, that you
The accompanying sidebar shows you how you can calculate know you can reach with the fuel remaining, plus a reserve.
the PNR before a flight. When in flight you must be assured of Whichever method you use to calculate it, never go past the
the weather at your destination before you proceed beyond this PNR unless you know you can safely land, otherwise there
point. You also need to monitor your fuel consumption, and may well be no returning from the flight.
Flight Plan Overdues Update
In the last issue of Vector we promised we would provide Number of VFR Flight Plans Filed 2003
regular feedback on how the VFR flight plan overdue 2500
statistics are trending. We also mentioned that there were 2000 2175 2150 2175
2021
some terminate-your-flight-plan reminder tools in the
Frequency 1500 1665 1468
pipe-line.
National Briefing Office statistics just to hand, show that 1000
there has been a two-percent drop in the number of 500
overdue VFR flight plans compared with those published
0
for March – a step in the right direction. Well done to Jan Feb Mar Apr May Jun
those of you who remembered to amend or terminate your
flight plans. There is still plenty of room for improvement Percentage VFR Flight Plan Overdues 2003
12
though!
10
A breakdown of the number of overdues by industry sector, 10 % 10 % 10 %
Percentage %
8 9%
the reason for the overdue and the number of flight plans 8% 8%
filed each month is detailed in the accompanying graphs. 6
The CAA, in conjunction with Airways New Zealand, has 4
just released an A2 poster and two types of stickers designed 2
to help you remember to amend or terminate your flight 0
plan. Entitled ‘Amend SARTIME or Terminate Flight Plan’ Jan Feb Mar Apr May Jun
they are based around a jigsaw puzzle and its missing piece; Reason for Flight Plan Overdues Terminated after SARTIME
the concept being that ‘no flight is complete until the flight 50 Failed to update SARTIME
Updated Sartime after SARTIME
plan has been terminated’. 45
Failed to terminate
40
The poster (see page 21 for a sample) is designed to raise ATC failed to pass on
Percentage %
35 *Other
awareness of the importance of amending or terminating 30
25
your flight plan. It should be displayed in a prominent place
20
within your organisation. 15
The A6 sticker (depicts the missing jigsaw piece) is intended 10
5
as a memory jogger only and should placed in locations that 0
pilots are likely to frequent after a flight eg, the toilet, Apr May Jun
* (Note that 'Other' includes IFR proceeding VFR failed to terminate, failure to request
kitchen, reception area or hangar. termination at an attended aerodrome, and not specified.)
The smaller A8 sticker contains the same information as
the larger one, but should be placed on items like the Flight Plan Overdues by Industry Sector Aero Club
Flying School
VFG, flight log clip board, aircraft dashboard or door. Both 50 Private
45
stickers are of the non-permanent variety so will not 40
*Other
damage the surface underneath when removed.
Percentage %
35
30
All of these products are available from your local CAA
25
Field Safety Adviser or flight training organisation. We hope 20
that you will use them. 15
10
Let’s keep working together to improve aviation safety 5
and to reduce National Briefing Office and Search and 0
Apr May Jun
Rescue costs, by minimising the number of overdues! * (Note that 'Other' includes commercial operators, RNZAF and Airways New Zealand.)
VECTOR July / August 2003 13Avgas – Specific
Gravity Values
W hile researching the Fuel Management GAP, Safety
Safety
Education & Publishing Unit staff discovered that the
specific gravity of New Zealand avgas was lower than the value
of 0.72 that was being used by most pilots for weight and
Seminars
balance calculations.
The best information available at the time of writing the GAP
indicated that the average specific gravity of fuel batches being
imported into New Zealand was 0.695. This value provides a – Weather Wisdom –
slight increase in useful payload when used in weight and
L
balance calculations. It was decided to bring this information ast year’s Av-Kiwi Seminar series Weather Wisdom was
to pilots’ attention in the form of an avgas quantity/weight so successful that the topic will be offered again this
conversion flow diagram on page 10 of the Fuel Management year at different venues.The focus will be on understanding
GAP. (This also meant amending all of the pre-determined our weather from an aviation perspective.
weight conversion factors in the diagram.)
Come along and listen to key presenter Erick Brenstrum
However, recent information obtained from fuel companies from MetService speak on this topic. He will be supported
indicates that a small amount of avgas with a specific gravity of by a local aviator (who will provide comment on local
0.715 is currently being imported into New Zealand. This has weather scenarios) and CAA staff.
effectively made the fuel conversion diagram in the GAP
inaccurate in some situations. Erick Brenstrum is the author of the highly acclaimed
New Zealand Weather Book. In this very readable book, he
In the interests of safety, we advise avgas users that the original clearly explains the weather, covering such things as how
value of 0.72 should be used for all weight and balance to interpret a weather map, and the wide range of weather
calculations. This way, the possibility of exceeding the aircraft patterns and processes that affect New Zealand.
MAUW is avoided should the heavier fuel be uplifted.
The seminars will involve a mixture of presentations and
The CAA apologises for this state of affairs, and we propose to practical work. The CAA will provide afternoon tea at
rectify the situation as follows: each venue, and will also be providing all attendees with a
A corrected avgas conversion flow diagram sticker (illustrated free copy of an interactive CD-ROM Weather Wise 2. This
here) using the original specific gravity value of 0.72 has been CD-Rom is about assessing flying weather, so you will be
produced to enable pilots to correct the GAP – or to stick in a able to further expand your knowledge and skills, using
prominent location for use as a quick fuel conversion reference. your home computer. A copy of the New Zealand Weather
Stocks of these will be circulated to all organisations that hold Book will also be awarded, as a spot prize, to one lucky
copies of the booklet via CAA Field Safety Advisers. All person at each seminar.
booklets currently held in stock by the Safety Education & Don’t miss this opportunity to learn more about one of
Publishing Unit will be corrected before distribution. the most influential factors affecting our flying
Note, we have been advised by the manufacturer that Aero environment. Dates and venues have now been set for
Scale navigation rulers sold since March 2003 (depicting the 2003 as detailed below.
new VNC scale) also use 0.70 for avgas conversion values Be there!
printed on the ruler’s back face. The manufacturer advises that
customised correction stickers will be made available to pilots
who have purchased one of these rulers through their local Seminar Venues
flight training organisation. Existing stocks will be corrected. To be held on the following Sundays from
12:30 pm – 4:00 pm:
1.58
AVGAS Hamilton Sun 17 August
litres
For AVGAS
calculations
Waikato Aero Club, Steele Road, RD 2 Hamilton
Lb
s (SG 0.72)
3.78 5.99
0.72 - follow the
arrow and
Dunedin Sun 24 August
4.54 US gals multiply
2.20 Otago Aero Club, Taieri Aerodrome, Mosgiel
- backtrack
7.19 the arrow
1.20 2.72
kg
and divide Palmerston North Sun 31 August
s
Imp gals Manawatu Districts Aero Club, Palmerston North
Aerodrome
3.27
14 July / August 2003 VECTORLifting
the Game
A t some recent CAA-sponsored safe-
ty seminars there was a fair bit of
talk about ‘lifting the game’ within the
general aviation community. Discussions
have mostly centred on improving basic
airmanship practices thereby lifting safety
standards. A lot of heads have nodded in
agreement to this at these gatherings.
But, as with most things in life, the real
change in behaviour needs to be at the
coal face. It is not just about agreeing or
committing in some notional way to do
things better at a meeting, it is about
doing things right, each and every day
we contemplate a flight. Yes, it is about a
change in attitude, and it is about being
disciplined enough to translate that A Supplement detailing the control thoroughly. Reading the Supplements
attitude into behaviour. zone’s parameters, arrival and departure and NOTAMs applicable to the intended
procedures, and associated radio freq- route is definitely an important part of
“…there were a number of uencies is always issued several months this process.
prior to the event to provide pilots with One of the aircraft involved in these
pilots who blundered their
Photographs courtesy David Jupp, Walsh Memorial Scout Flying School
as much notice as possible. Furthermore, recent airspace incursions came from the
way into Matamata CTR on-going trigger NOTAMs referring to lower North Island and it was pretty
the Supplement are issued daily once the evident that neither the Supplement and
oblivious to its presence…” airspace is activated. NOTAMs, nor the weather forecast had
Recently, a CAA staff member attended As you can probably guess, this year, as in been consulted. Others came from closer
the Walsh Memorial Flying School at past years, there were a number of pilots at hand, but still without a clue that
Matamata and was concerned by the who blundered their way into Matamata Matamata aerodrome was very different
lack of basic airmanship displayed by CTR oblivious to its presence only to and very busy at this time. Fortunately,
some of the pilots visiting Matamata find themselves in the middle of a lot of Airways New Zealand staff members are
during the event. It seemed that they other aircraft activity. good at handling these situations and
had not checked the AIP Supplement and Obviously, the aircraft involved were managed to keep the traffic flowing
NOTAMs before commencing their itinerant aircraft making only a short safely.
flight to Matamata. The reasons for his stopover at Matamata, which presumably Usually, the offending pilots end up
concern were valid as there was, and has means they were on a cross-country talking away on the aerodrome’s second-
been for many years, an ATC presence at flight of some distance. It is both a CAA ary frequency as they attempt to join the
the airfield in the form of a control zone rule requirement and basic airman- aerodrome circuit. It isn’t good to see
(Matamata CTR/D) for the two-week ship to plan such flights, which means licensed pilots making right fools of
duration of the school. having studied the relevant documents themselves in front of a large community
of budding aviators – all for the lack of a
bit of preparation and planning.
The observers to these unprofessional
incidents are the sixty or so students
attending the school, and around forty
experienced instructors, aviators and air
traffic controllers. Typically, there are
about 20 aircraft based at the school.
Parallel runway operations take place in
conjunction with four training areas in
the vicinity. At any one time there can
be eight to ten aircraft airborne and
others preparing to leave. Weather
permitting, flying takes place pretty
much continuously and sometimes at
Continued over ...
VECTOR July / August 2003 15You can also read
