Mindset
Can Be a Killer — A Fatal Ditching
My dictionary defines
‘mindset’ as a fixed opinion or state of mind formed by earlier
events. The real safety-related problem is that once we humans misinterpret
or misunderstand something heard or seen it is very difficult for us to
realise that we have made a mistake and correct it by re-evaluating the
original mental input. Map reading from the air can provide frequent examples
of this error sequence. You know where you expect to be in relation to the
track line on your chart. You see a ground feature, or a combination of
ground features, that looks like the features on your map so, there you are!
A fix on track! Unfortunately it is all too easy to make the features fit the
chart and not realise that you are actually off track until you are well and
truly lost.
I believe that the following accident report illustrates just how
serious can be the results of mindset where a
pilot was possibly led astray by a series of events before flight. This may
have led him to fail to recognise the most likely cause of the problem with
his aircraft.
I have no intention of blaming the pilot for the accident in which he
and his wife died. The purpose of this article is to alert others to the
hazards of mindset.
The pilot planned to take his wife for a local
flight from Liverpool Airport in a Piper PA-28-161 Cherokee Warrior II on 4th
July 2004. He visited the airfield in the morning to confirm that the weather
was suitable, before returning an hour later with his wife. During the
pre-flight inspection the pilot discovered that a fuel sample taken from the
aircraft contained a considerable amount of water and some black debris. He
returned to the clubhouse with the contaminated sample and remarked that this
was the third or fourth water contaminated sample he had taken from the
aircraft. He asked for the strainer to be kept at the club to be shown to the
aircraft owners and borrowed another strainer before returning to continue
his pre-flight on the aircraft. A club instructor saw the pilot drain off
several more fuel samples from one wing before he obtained a clear
sample.
The aircraft took off and departed to the south, climbing towards a
VRP at Chester. The pilot changed to Liverpool Approach and reported leaving
the zone at Chester. Just thirty minutes later he made a ‘PAN’
call to Liverpool Approach saying that he was ‘OFF WALLASEY’
losing altitude and power. He was given heading information for a direct
return to Liverpool Airport. Half a minute later he broadcast a
‘MAYDAY’ call saying he was ditching the aircraft.
Two training aircraft overflew the impact site and could see where
the aircraft had entered the water but there was no sign of the aircraft or
any wreckage. Two nearby lifeboats were on the scene very quickly but could
not find the aircraft. The aircraft was located as the tide fell and two
bodies were recovered by divers.
The aircraft had suffered an unexplained engine
failure two months before the accident flight. This resulted in a forced
landing into a field. The aircraft was flown out of the field after fuel had
been removed to reduce the aircraft weight. This fuel was uncontaminated and
later used in other aircraft. No fault was found with the engine and the
failure remained unexplained. However, the conditions at the time of that
forced landing indicated the possibility of ‘Moderate icing at cruise
power and Serious icing at descent power’ according to the carburettor
icing chart.
The weather at Liverpool Airport at the time of the fatal accident
was recorded as surface wind 290/15 kt, visibility 10 km, scattered cloud at
2,000 feet, temperature 16°C, dewpoint 10°C and pressure 1012 mb. The
temperature at 2,000 feet was estimated at 12°C with the relative humidity at
67%. These conditions were conducive to severe to moderate carburettor icing.
The conditions at the ditching site were high tide with a water depth of 8
metres, wind north-westerly force 4, sea state moderate with a 1 metre swell.
The direction of the swell was confused because of sandbanks in the
area.
When the aircraft was found both occupants were still wearing lap and
diagonal harnesses that were still secured and the entry door was open. The
wreckage was recovered to AAIB at Farnborough for detailed examination. The
damage was extensive, indicating impact with the sea at a pitch attitude of
20° nose down, about 5-10° left bank and some right yaw. The impact collapsed
the nose gear and caused extensive damage to the leading edges of both wings
with the right wing separating and the tail twisting to the left opening up
the right rear fuselage. The engine had been forced rearwards, pushing the
instrument rearwards and causing deformation of the cabin and its roof. The
propeller was undamaged indicating that the engine was not under power at
impact. The throttle was at idle and the mixture was set to lean. The
position of the carburettor heat selector could not be determined with
certainty. The electric fuel pump was ON, the flaps were up and the pitch
trim was at neutral. The stall warning circuit breaker was tripped but this
could have occurred before the accident or at impact. The remains of the fuel
system did not show any evidence of pre-impact contamination.
The seats were still secure, undeformed and had not moved forward,
but the instrument panel had moved far enough aft to impact both occupants.
There was no evidence of any pre-impact mechanical failure of the engine or
its components.
Detailed
checks of the refuelling operation at Liverpool Airport, including other
aircraft that received fuel from the same bowser both before and after the
refuelling of the accident aircraft, did not reveal any evident of fuel
contamination. The fuel sample taken from the accident aircraft before it
flew was taken for specialist analysis. This sample contained about 7.5 ml of
water and 1 ml of fuel, with some debris in the water and a layer of black
substance at the fuel/water interface. There was no evidence of
microbiological contamination.
Post mortem examination of the pilot and passenger revealed serious
injury to both on impact but the final cause of death was drowning.
A Précis of the AAIB Analysis
The origin
of the water in the fuel sample left at the clubhouse remains a mystery. It
could not be determined whether water in the fuel caused the engine failure
that occurred about 30 minutes into the flight when the pilot would be
expected to be changing fuel tanks.
There is no clear reason for either of the engine failures suffered
by this aircraft but on both occasions meteorological conditions were such
that there was a risk of moderate to severe carburettor icing and carburettor
icing cannot be discounted as the cause of the engine failures. The aircraft
was beyond gliding range from land when the engine failed. Preparation time
was short but if the pilot had been able to reduce the speed to a minimum
groundspeed without stalling it is possible that both occupants would have
survived the ditching and been picked up by the rescue services. The aircraft
heading at impact could not be determined but the severity of impact suggests
that it was out of wind. The difference in groundspeed could have been as
much as 30 kt if the ditching had been made into wind. The touchdown speed
could also have been reduced by use of flap.
Wearing lifejackets and the carriage of a liferaft would not have
prevented the deaths of the occupants in this accident. A ditching in
reasonable conditions should be survivable and most people do survive the
impact. Many lives are lost after ditching as a result of the time spent in
the water without appropriate survival equipment.
Editor’s Comments
The above
article is a summary of the very comprehensive AAIB Field Investigation
Ref:EW/C2004/07/01 published in AAIB Bulletin 1/2005 and also available on
the AAIB website at www.aaib.gov.uk. This source is gratefully
acknowledged.
The investigation of fatal aircraft accidents often involves trying
to put oneself into the pilot’s situation and attempting to reach some
sort of conclusion as to what the pilot was doing and thinking before the
accident happened. In this accident there is no doubt that conditions were
conducive to moderate to severe carburettor icing and it is reasonable to
conclude that this aircraft had previously suffered from carburettor icing in
similar conditions. There is no evidence available as to whether the pilot
had or had not selected carburettor heat ON before the aircraft ditched. My
suggestion is that the pilot was well aware that there had been a
considerable amount of water in the fuel tank (or fuel tanks?) before the
flight began. It is likely that the engine began to lose power at about the
same time as he changed tanks. This combination could easily lead the pilot
to the conclusion that the problem was due to fuel contamination. His efforts
to resolve this apparent problem would probably involve changing tanks again,
selecting the electric fuel pump to ON and checking the fuel tank contents.
All of these actions would have been fruitless if the real cause of power
loss was carburettor icing.
It would have taken a considerable mental jump to discard the idea of
fuel contamination and look for another cause of the engine failure,
particularly while at a fairly low altitude and faced with the certainty of a
ditching if the problem was not resolved. The fact that the pilot’s
wife was on board the aircraft would heighten the pilot’s level of
stress.
All of these comments are based on nothing more than supposition and
are not in any way critical of the pilot’s actions.
I suggest it is possible that this accident resulted, at
least in part, from the mindset of the pilot brought about by his discovery
of considerable contamination of the fuel before he began this flight. Such a
mindset is very persuasive and difficult to overcome, particularly in a
stressful situation. Pilots need to be aware of the possibility of making an
incorrect deduction in these circumstances.
Text and Photographs © 2007 Gremline & Hill House
Publications, unless otherwise stated.
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