CAP 222 (Modified), G-GZOZ 04

AAIB Bulletin: 4/2006
Aircraft Type and Registration:
CAP 222 (Modified), G-GZOZ
No & Type of Engines:
1 Lycoming AEIO-360-A1E piston engine
Year of Manufacture:
Date & Time (UTC):
8 July 2005 at 1415 hrs
White Waltham Airfield, near Maidenhead, Berkshire
Type of Flight:
Persons on Board:
Crew - 1
Passengers - None
Crew - 1 (Fatal)
Passengers - N/A
Nature of Damage:
Aircraft destroyed
Commander’s Licence:
Airline Transport Pilot’s Licence with Flying Instructor
Commander’s Age:
43 years
Commander’s Flying Experience:
10,149 hours (of which 115 were on type)
Last 90 days - 221 hours
Last 28 days - 49 hours
Information Source:
AAIB Field Investigation
The experienced aerobatic pilot had briefed to fly four
anti-clock-wise rotational movement when viewed from
different unlimited aerobatic manoeuvres, practising
above. The pilot was fatally injured on impact.
three of each whilst being watched by his aerobatics
Pilot’s flying experience
instructor. When practising the fourth manoeuvre, a
knife-edge spin1, for the third time, the aircraft entered
The pilot was a current Boeing 747 commander. In
an inverted spin which was not part of the planned
addition to his UK Airline Transport Pilot’s Licence,
The aircraft continued spinning until it
he held an FAA Commercial Pilot’s Licence and a
impacted the ground. It struck the ground in an inverted
New Zealand Private Pilot’s Licence. He started flying
attitude, with a high vertical rate of descent and with an
competition aerobatics in about 1995, winning the
Standard Nationals aerobatic competition in 1997, in a
A knife-edge spin is not a true spin because the wings are not
stalled. Instead, the aeroplane is deliberately yawed and it rapidly
rotates in pitch about its lateral axis, under the influence of elevator
and gyroscopic forces.
Pitts S1D. He then moved on to advanced aerobatics
in 1999 and became the National Aerobatic Champion
at this level in 2002. He had been flying ‘unlimited
AAIB Bulletin: 4/2006
aerobatics’2 in G-GZOZ since 2003 but he continued to
aerobatics in the overhead are 2,300 ft agl and 500 ft agl
compete at the advanced level. He also held a Flying
respectively. The weather minima required are 2,500 ft
Instructor rating and a Display Authorisation to perform
cloud base and 5 km visibility.
aerobatics down to a base height of 500 ft agl.
The weather was good with a surface wind from 020° at
Nine months before the accident the pilot frequently
08 to 12 kt, a visibility of 10 km or more and broken cloud
practised aerobatics. He then stopped flying aerobatics
at 3,200 ft and 4,500 ft agl. In accordance with normal
on a regular basis whilst he completed, with his airline
practice, the flight was ‘booked out’ on a ‘Waltham
employer, an aircraft type conversion course followed
Based Aircraft’ sheet, showing a planned departure time
by a command course. One month before the accident,
of 1400 hrs.
the pilot resumed his previous aerobatic continuity and
The pilot was described as looking fit and well that
was again flying aerobatics frequently.
morning. People who had lunch with him said he was
Other aerobatic types he had flown included the
in good spirits and in a happy mood. In the afternoon,
Chipmunk, CAP 10, Tiger Moth, Harvard, Extra 200,
the pilot briefed with his instructor, for his second flight
Sukhoi 29, Yak 52, various types of Pitts, and the Cessna
of the day. This flight was to practice four different
150 Aerobat.
manoeuvres, flying three of each, all of which he had
flown before on various occasions. The last manoeuvre
History of flight
was to be a knife-edge spin.
On the day of the accident, the pilot flew one flight in
G-GZOZ prior to the accident flight. He had first flown
The first three manoeuvres were flown without any
in the morning to practise some other unlimited aerobatic
problems. He then planned to fly the knife-edge spins,
manoeuvres. On both occasions he was provided with a
in order to practise the correct amount of aileron to use
ground based radio critique, on a quiet frequency, by the
during the manoeuvre. He intended to complete only
part-owner of the aircraft who was a very experienced
one rotation in pitch during each knife-edge spin. The
aerobatic flying instructor and international aerobatic
first repetition was not balanced and progressed into a
competitor. The instructor was positioned outside the
positive flick roll, (sometimes called a snap roll) from
flying club house, about 1 km from the crash site.
which the aircraft recovered normally. The second was
flown satisfactorily, with good balance, but the rotation
Both flights were flown overhead White Waltham
rate was a little slow. His instructor thought this was
Airfield, in pre-booked slots of 20 minutes.
because he was not putting in full-forward control
Waltham flying orders state that aerobatics overhead the
column. His instructor passed this advice to him by
airfield are to be confined to that part of the aerodrome
radio. He stated that he accepted the advice and set up
traffic zone that is to the west of the Heathrow Control
to try one more knife-edge spin.
The maximum and minimum heights for
The set up and entry to the third knife-edge spin was
The most proficient aerobatic skill level of the class sequence:
standard, intermediate, advanced and unlimited.
flown correctly, at a height of approximately 2,300 ft agl.
After one complete rotation in pitch, no recovery action
AAIB Bulletin: 4/2006
Other witnesses
was evident. After a further half a rotation in pitch, the
instructor called “recover” over the radio. He expected
Many other eye witnesses saw the accident. The majority
the aircraft to enter a vertical dive from which it would
of them were outside the flying club at White Waltham,
then recover. The pilot did not reply to this call.
near the instructor. They reported seeing the aircraft
doing aerobatics and then saw it enter a spin. Most
The aircraft then continued for a further half to
identified the spin as inverted. They also stated that
three-quarters of a rotation in pitch, before going onto
there was no change in attitude or rate of rotation, after
its back and entering an inverted spin at approximately
the first few turns of the spin, before the aircraft went
1,800 ft agl. The aircraft continued to spin inverted until it
out of sight and impacted the ground. Another witness
impacted the ground. Because this inverted spin initially
was flying into White Waltham while the aerobatics
had a slow rate of descent with a ‘flat’ pitch attitude, it
were taking place. He stated that he saw the aircraft at a
appeared to the instructor to be one in which right rudder
height of approximately 1,000 to 1,500 ft in a spin. After
was applied. (A right-rudder inverted spin is generally
observing it for a few turns, he soon became aware that
flatter than a left-rudder inverted spin.) Being aware of
if it did not recover soon, it would crash. He added that
the manoeuvre the aircraft was then in, the instructor
“it continued spinning with no visible attempt to alter the
transmitted over the radio “change feet and stick back”.
attitude of the ‘plane.” He did not notice if the spin was
He may have said this twice but there was no reply.
erect or inverted.
The aircraft was by then at a height of approximately
1,500 ft agl. If recovery action was initiated without
Another witness was taxiing his aircraft out to
delay, this should have been enough height to recover
Runway 03, at White Waltham. He stated that, as he
from this inverted spin.
was approaching the end of a line of parked aircraft, he
suddenly became aware of an aircraft spinning inverted
The aircraft continued to spin inverted until it went out of
and rotating to the left. At the time he estimated the
sight to the instructor behind a small rise on the airfield,
aircraft’s height to be approximately 600 to 800 ft agl.
where it impacted the ground. Whilst the aircraft was in
The aircraft appeared to be approximately 45º nose down
the inverted spin, the instructor did not see any change
with the propeller blades rotating slowly. He continued
in aircraft attitude or rate of rotation to indicate that there
was any input to the flying controls. He also did not hear
to watch the aircraft until it impacted the ground.
any radio transmission from the pilot but he also stated
The knife-edge spin
that his own transmission could have blocked those of
the pilot.
A knife-edge spin is not a true spin, because it is not a
‘classic’ autorotation; for a successful knife-edge spin,
The airfield’s emergency services were quickly in
the angle of attack at the wings must remain negligible.
attendance and they confirmed that the pilot had not
During the manoeuvre the aeroplane falls vertically and
survived the accident. Paramedics from the resident air
rotates in pitch about its lateral axis, (a motion sometimes
ambulance, attended soon afterwards. In addition, fire
described as tumbling), as it descends. The aircraft will
vehicles from Maidenhead attended the scene.
lose about 200 ft of height in the first turn but this height
loss per turn tends to increase with successive turns.
AAIB Bulletin: 4/2006
In an aircraft with a clockwise turning propeller, a
pushed too slowly, the aircraft will accelerate with
knife-edge spin is usually entered from a stall turn
the same result. When the control column is pushed
to the left. Initially, a stall turn is flown until, when
forward, the pilot must apply aileron to keep the wings
entering the descent, the moment arises when the pilot
in the vertical plane. The task with the ailerons is to
should apply opposite rudder to stop the yaw. Instead,
balance the aircraft so that it falls straight downwards
left rudder is maintained. This makes the aircraft’s
with the wings at right angles to the ground. If an angle
nose swing through the vertical to about 45° past the
of attack is generated by using too much aileron, the
vertical. With the nose in this 45° nose-up attitude,
aircraft may enter a flick roll. Too much left aileron
full forward control column is then smoothly applied to
may lead to a positive flick roll; too much right aileron
start the pitching motion. With high engine rpm, this
may lead to a negative flick roll.
pitch-down generates a large gyroscopic force which
will assist the applied left rudder in holding the nose
The recovery procedure is always the same; apply
up against gravity. The forces involved are illustrated
opposite rudder and move the control column centrally
at Figure 1.
It is possible to reduce the power initially,
to reduce the gyroscopic effects, before applying
the recovery controls but this will also reduce the
effectiveness of the rudder in cancelling the yaw.
It is possible to enter an inverted spin from a knife-edge
spin if right rudder is applied while full forward elevator
is maintained.
Aerobatic limitations
The aircraft was cleared for aerobatic manoeuvres,
including unlimited aerobatics, when complying
with the limitations prescribed under the Aerobatics
Category, up to its MTWA. Calculations show that the
Figure 1
aircraft’s weight was below the MTOW and the CG
Knife Edge Spin illustration
position was within the required limits.
Spin recovery technique
The control column does not need to be pushed
However, if there is a delay before
The following information was included in the
pushing whilst on the knife edge, the aircraft’s forward
‘Approved Airplane Flight Manual and Operating
speed will accelerate and the aircraft will straighten
Handbook’ for the aircraft (See Figure 2):
due to the effect of the stabilising effect of the fin.
The pilot will then be exposed to an increased amount
of negative g and the manoeuvre could become a
descending outside turn.
If the control column is
AAIB Bulletin: 4/2006
Recovery from unintentional spins
The lost of altitude is about 330 ft (100 m) per turn, and 1000 ft (330 m) for the recovery.
Before applying the recovery procedure, it is necessary to identify the nature of the spin, UPRIGHT
The spins are very predictable and the recovery procedure is conventional:
Power ........................................................... idle
Ailerons ........................................................neutral
Rudder .........................................................full opposite to the spin
Elevator .......................................................neutral for upright spins slightly
backward for inverted spins
Figure 2
Excerpt from Approved Airplane Flight Manual and Operating Handbook
Medical information
certification expected within 12 months. However, this
did not happen due to funding issues. As delivered,
The pilot held a current JAA Class 1 medical certificate
the aircraft was registered in France as F-WWMX. In
with a limitation requiring him to wear distant vision
May 2005 it was transferred to the UK register as G-
lenses while flying and he was wearing a pair of spectacles
GZOZ, operating on a CAA Permit to Fly.
at the time of the accident. The post mortem examination
It was
registered as a CAP 222 (Modified) because it would
carried out by a consultant aviation pathologist, revealed
probably vary from any subsequently certificated
that the pilot had died instantly from multiple injuries
CAP 222 should JAR 23 type certification be obtained.
resulting from a severe vertical force. The pathologist
concluded that there was no evidence of any medical
The aircraft had accumulated 475.3 hours at the time of
condition or toxic substance that may have caused or
the accident. It was fitted with a three-bladed propeller
contributed to the accident.
with a constant speed unit and a microprocessor based
engine management system.
Aircraft information
This system displayed
engine rpm, exhaust gas temperature, manifold pressure,
The aircraft type was derived from the Giles G202. The
fuel pressure and cylinder head temperature on a flat panel
French aircraft company, CAP Aviation, undertook to
display. In addition to displaying these parameters, it
take on the design as a CAP project and obtain JAR 23
was able to store the values in non-volatile memory and
certification, renaming it the CAP 222. The accident
alert the pilot to significant variations.
aircraft, constructor’s number C03, was built in 1998
and delivered as an uncertified aircraft but with JAR
AAIB Bulletin: 4/2006
Engineering investigation
or restriction was found. In brief, no evidence of any
flying control system problem was found.
The aircraft had struck the ground inverted in a fully
developed inverted spin to the left, ie to the right
There were no obvious witness marks identifying the
relative to the aircraft’s vertical axis. The wings were
position of the ailerons or elevators. However, clear
approximately level at impact, and there was very little
marks were found on the rudder pedal linkage which
travel over the ground. The impact was substantially
indicated that full right rudder had been applied at
nose down, after which the top of the fin struck the
ground impact.
ground and, due to the rotation of the aircraft, there
was some sideways movement of the rear fuselage and
empennage. The pilot’s harness had been fastened at
Inverted spin recognition and recovery
impact but the accident was not survivable.
The accident pilot’s aerobatics instructor commented
Evidence of engine speed and power was obtained
that he had seen the pilot practise planned inverted spins
from the damage to the propeller. This showed that
before, but he had not seen him enter an unplanned
at ground impact, the engine had been turning at low
inverted spin from any other aerobatic manoeuvre.
power, consistent with idle, and had stopped in less than
Because the inverted spin was inadvertently entered at
one third of a rotation. The non-volatile memory, in
a low height, the pilot only had a few turns to identify
the electronic engine management system fitted to the
that he was in an inverted spin, identify the direction
aircraft, was returned to its manufacturer in order for the
of the spin and apply the correct recovery technique
data to be recovered. The manufacturer confirmed that
in time to recover from the ensuing dive and avoid the
prior to impact, the engine was working normally and
operating at idle rpm.
ground. In this case, it is estimated that he had no more
The aircraft was recovered to the AAIB facility at
The elapsed time between spin entry and initiating a
Farnborough for a more detailed investigation.
successful recovery was, perhaps, as little as 5 seconds.
pre-impact discontinuity was found in any of the primary
This was a very short time in which to resolve any
flight control systems, much of which could still be
unexpected confusion.
than three turns in which to commence the recovery.
functioned. All the breaks identified had been caused
A turn indicator is the only instrument that can be used
in the impact or were deliberate cuts made when the
wreckage was recovered.
to identify the direction of an erect or an inverted spin.
The aircraft was well constructed (it was a factory-built
was no requirement for one to be fitted because it was
demonstrator) and the control runs were well laid
only cleared for VFR flight. In addition, a turn indicator
out. They did not appear particularly vulnerable to
would not necessarily be fitted to an aerobatic aircraft
interference from foreign objects. No extraneous objects
because the instrument panel might not have sufficient
were found in the wreckage and the front seat harness
installation space. Also, the delicate gyro assembly in
was adequately stowed. The possibility of a control jam
the turn indicator would be susceptible to failure whilst
could not be entirely ruled out but no evidence of a jam
flying high-performance aerobatics.
There was no turn indicator fitted to G-GZOZ and there
AAIB Bulletin: 4/2006
If the direction of an inverted spin needed to be
unintentional and the pilot’s intention was to complete
identified in an aircraft with no turn indicator fitted, the
only one rotation in the knife-edge spin. In fact, he did
pilot would have to look over the nose of the aircraft and
between one and a half and two and a quarter rotations.
use visual cues alone. This introduces the possibility
This suggests that the pilot’s difficulties may have started
of confusion, particularly if the entry was sudden and
during the knife-edge spin.
unexpected. Another generic technique to identify turn
direction is to remove any foot pressure from the rudder
After his previous attempt, the pilot had been advised to
pedals, press each pedal in turn, determine which pedal
increase the rate of rotation in the knife-edge spin. The
requires more effort, and then push the ‘heavy’ pedal.
rotation rate he achieved on his third attempt is estimated
However, the CAP 222 Flight Manual states that during
at about one turn in less than a second. The pilot’s head
spins, there is no aerodynamic pressure on the controls,
was about 1.2 m from the axis of rotation, which passed
so the technique could have been ineffective on this
through or close to his body. At 1 second per rotation, the
aircraft type.
acceleration at his head would have been minus 4.8g.
Pilot incapacitation
At 0.8 seconds per rotation, his head would have been
The accident occurred because the pilot did not recover
subjected to a negative acceleration of 7.5g whilst his
from the inverted spin. In the absence of evidence for
feet would have been close to the axis of rotation; see
a mechanical problem, this suggests he may have been
Figure 3 below:
confused or incapacitated. Entry to the inverted spin was
Acceleration experienced at the head = Rω2
At 0.8s per revolution, ω = 7.85 rad/s
Acceleration = 74 ms-2 = 7.5g
Centrifugal force
Angular velocity: ω
R = 1.2m
Axis of rotation
Figure 3
Forces acting on pilot’s head
AAIB Bulletin: 4/2006
Positive g sends a pilot’s blood towards the lower body;
would not have been unlikely even in the absence of the
negative g sends the blood upwards towards the head.
acceleration-induced physiological effects. In addition,
The equations above illustrate that a small increase in the
the transition from the knife-edge spin to the inverted
speed of rotation would have brought about a significant
flat spin is likely to have been accompanied by vestibular
increase in the acceleration experienced.
overload; the pilot may have experienced illusory
feelings of rolling in addition to the actual gyrations
Negative g is uncomfortable and less well tolerated
involved in the transition. This sensation is familiar to
than positive g. Exposure for more than six seconds
the competitive aerobatic community. They refer to this
to between minus 4g and minus 5g is reported to cause
feeling as “wobbly head”.
confusion and unconsciousness3.
If the pilot did have normal levels of cognitive function
As an experienced aerobatic pilot, the accident pilot
during the inverted spin, he would have been faced with
might have been expected to tolerate minus 4g relatively
an increasingly alarming situation. Given that he was a
well, at least for a few seconds. If he was unused to
fairly experienced aerobatic pilot, it is unlikely that he
higher levels of negative acceleration, a sudden and
panicked. But the preceding few seconds would have
unexpected exposure to minus 7.5g could have been very
been confusing as well as painful and disturbing, and
disturbing and painful, delaying his attempt to recover,
he would have been presented with a dilemma: Should
making that attempt inaccurate and, perhaps, provoking
he persevere with a control strategy that is failing or
an unthinking retardation of the throttle.
change a strategy that might be about to work? In such
a situation, unless there is a clear, positive, indication
After possibly as long as 1.5 seconds at minus 7.5g, the
that the strategy is wrong, perseverance may persist by
pilot may then have experienced even higher levels of
default – even if it appears clearly inappropriate to an
negative g, very briefly, as the aircraft transitioned to
observer who has the benefits of distance, hindsight, and
the inverted spin, due to the sudden increase in drag
a comfortable 1g, upright viewpoint.
from the wings. Once stabilised in the inverted spin,
the pilot would then have been exposed to a lower level
In summary, the pilot may have been exposed to an
of negative g which might have had continued effects on
unexpected, disturbing and painful level of negative
his cardiac efficiency and, therefore, on cerebral blood
acceleration by his attempt to make the knife-edge spin
flow and cognitive function.
slightly brisker in terms of speed of rotation. As a result,
his exit from the manoeuvre was delayed and the aircraft
The unintentional entry into the inverted spin would, of
entered an inverted spin. His cognitive efficiency was
itself, have presented the pilot with a challenge in terms
likely to have been impaired by: the initial negative
of determining the direction of the manoeuvre and the
acceleration, any transient accelerations experienced in
correct recovery action. A response time of a few seconds
the transition from the knife-edge spin to the inverted
spin, and by the continued exposure to negative
acceleration during the inverted spin. The entry to the
Aviation Medicine (third edition) by Air Vice Marshall J Ernsting,
Air Commodore A N Nicholson and Air Commodore D J Rainford
(eds). Butterworth-Heinemann, Oxford, 1999.
inverted spin was likely to have been confusing, in terms
of both visual and vestibular sensations, so that a rapid
AAIB Bulletin: 4/2006
corrective reaction was not likely. If the pilot did recover
any indications of recovery consistent with application
normal levels of cognitive function as the inverted
of the control movements required to effect recovery.
spin progressed, he would have faced an increasingly
Moreover, pro-spin rudder was still applied at ground
alarming situation with no clear options for recovery.
impact. No reason for this failure to recover could be
positively identified. However, the circumstances of
the accident could be explained by some form of brief
During a practice session of unlimited aerobatic
and temporary pilot incapacitation.
manoeuvres at low altitude, the aircraft entered an
confusion, disorientation and lack of time may have
unplanned inverted spin. The aircraft did not exhibit
been contributory factors.
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