ACCIDENTS INVESTIGATION BRANCH (CIVIL AVIATION)

Accident to Sabre 4. XB.647 on 8.7.54

1.   Circumstances

Whilst overshooting the airfield at R.A.F. Jever, Germany, the undercarriage
was seen to retract but the dive brakes remained "OUT".   A climbing turn to port
was then carried out at a low airspeed with the dive brakes still "OUT".   The
aircraft climbed to about 1500ft. at the same time turning through 90°.   It was
then seen to flick rapidly, after which it continued to roll and lose height until
it hit the ground.   The aircraft was destroyed and the pilot was killed.

2.   The Aircraft

The aircraft was built by Canadair Ltd. in September, 1953.   It had. flown
46 hours since new.   The General electric J.47 turbo jet engine was installed
during construction and had run 46 hours since installation.   The maintenance
records showed that the aircraft was serviceable when it took off.   The estimated
all up weight at the time of the accident was about 13,000 lb. and the C. of G.
24.9% m.a.c. (aft 1imit is 26.57% m.a.c.).

3.   The Pilot

The pilot, age 24, held an 'Average' flying assessment and his total flying
experience as first pilot in all types amounted to 277 hours.

His experience in the Sabre 4, was 64 hours.

4. The Weather

The weather at the time was fine, with excellent visibility and is not
considered to have any bearing upon this accident.

5.   Investigation

The general disposition of the wreckage indicated a fairly slow speed impact.
The first point of impact was a large tree with the starboard wing tip, whilst the
aircraft was ins nose down attitude.   The wreckage was slightly burnt by the
impact fire. The condition of the compressor and turbine was consistent with the
engine rotating at high speed when impact with the ground occurred.   [See below]   The tailplane,
rudder and aileron trim was approximately neutral.   There was no evidence of any
pre-impact structural failure of the airframe or malfunctioning of the flying
controls.   The undercarriage, flaps and air brakes were in the retracted position
when the aircraft struck the ground (witnesses state that the airbrakes were in
the "OUT" position in the early stages of the overshoot).   No useful evidence was
gained from the damaged cockpit owing to the severe damage sustained to all
controls and switches.

6.   Observations

This accident happened, after a climb away from a practice overshoot in fine
weather.   Several witnesses saw the aircraft with undercarriage and flaps
retracted but with air brakes OUT.

According to AP4503D (Pilot's Notes) para. 62 the aircraft is extremely
sensitive to "G", fractional amounts will produce a noticeable increase in the
normal stalling speed of approximately 110 knots.

Power controls with artificial feel do not transmit air loads to the control
column and in consequence the only warning of a stall being slight buffeting of
the airframe which occurs some 5 to 10 knots above the critical speed.   An aircraft
in a turn with too low a power setting if not handled carefully could quickly drop
a wing and roll either into or out of the turn, the rate of descent would be high
and considerable height would be lost during recovery from the stall.

With the three position air brake control, pilots report that it is quite
possible to place the switch in "NEUTRAL" when selecting air brakes "IN" and it
is only when the aircraft fails to accelerate away at the recommended, power
setting of 85/90% RPM for a light and clean aircraft that a check shows the switch
set to NEUTRAL.   At this stage of events the drag caused by the extended air brakes
at low power settings could reduce the aircraft's speed to a dangerously low figure,
the power controls would give no indication of an impending stall and the nose
trim caused by too late an retraction of the airbrakes could have brought about
a state of affairs from which recovery could not be effected in the height available.

At the time of this accident the Sabre Mk.4 (without leading edge slats)) was the
latest version to go into squadron service and it is interesting to note that since
this accident took place there has been at least one other accident to a Mk.4 Sabre
in Germany which was attributed to loss of control following a stall at low
altitude.   Signal AB.36EA dated 6/8/54. refers.

7. Conclusions

It is probable that the pilot lost control during a low speed turn with
insufficient height in which to effect a recovery.   Failure to select air brakes
"IN" during the early stages of the overshoot may have been a contributory factor.


Accidents Investigation Branch
(Civil Aviation)
Ministry of Transport and Civil AviationChief Investigating Officer
20th January, 1955.for Chief Inspector of accidents.

Circulation: -

A.D.P.A.
R.D.  Structures)
R.D.A. (Defects)

CONFIDENTIALR.A.F.   FORM   412
(Pages 7 and 8)
(Revised January, 1950)

25.   Conclusions of the Court (Note 10)

A.     On the 8th. July, 1954 Flying Officer Jack took off at 0806Z
to carry out, as authorised and briefed, three Radio Compass
letdowns followed by a V.H.F./D.F. controlled descent.
During these exercises nothing unusual was noticed.   He
overshot from the controlled descent apparently normally, the
undercarriage was seen to retract and the dive brakes to
remain "OUT".   About three quarters of the way down the
runway the aircraft was seen to exercise a climbing turn to
port at low speed with the dive brakes "OUT ".   The aircraft
climbed from seven hundred feet to an estimated fifteen
hundred to two thousand feet, at the same time turning
through approximately ninety degrees.   It was then seen to
flick rapidly, after which it continued to roll and lose
height until it hit the ground, killing the pilot and
and completely destroying the aircraft.

B.     The Court finds that there is no conclusive evidence as to
the precise reason for the accident, but considers that the
most probable cause was the pilot losing control of his
aircraft in a low speed turn.   It is characteristic of a non
slotted Sabre to flick and then go into a spiral dive under
these conditions.   Attention is drawn to the evidence of
the 9th. witness whom the court considered to be the most
reliable witness produced.   He was the only witness who saw
the whole sequence of events from the start of the overshoot
to the actual crash.   It is pointed out that although this
officer is a member of the Royal Air Force Regiment he is
extremely interested in flying and is about to commence
pilot training himself.   The evidence of the 2nd. witness,
is not considered so conclusive, as, although he is a Sabre
pilot he did not see the aircraft during the overshoot or
the ensuing turn, and due to his distance from the aircraft
the court do not consider his evidence as to the direction
of the roll conclusive.

The court also considers that the failure to *select dive
brakes "IN" during the early stages of the overshoot was a
contributing factor.   The evidence of the 8th. witness and
the A.I.B. inspector's estimate as to the speed on impact
both point to the aircraft being at a very low speed in the
turn.

C.     There is no evidence of any technical failure.

D.     Flying Officer Jack was killed on impact.

E.     Sabre Mk.4 XB.647 is category 5 (scrap) and Safety Equipment
and Flying Equipment worn by Flying Officer Jack was
totally destroyed.

F.     There were no injuries to civilian personnel.

G.     There was considerable damage to standing crops and several
trees.   The exact extent of the damage cannot be ascertained
until the wreckage and widely scattered live ammunition has
been cleared.   [See below].

H.     No other service personnel received injuries.

J.     It is unable to allocate responsibility or apportion blame
other than a possible error of judgement on the part of the pilot.

K.     There are no relevant recommendations that it can make.

Signature of
President     B.G. MEHARG   Wg.Cdr.................


(...  L.  BYRAM Flt.Lt......................
Signatures(...  G.C.  WILKINSON   Fg.Off..........
of      (............................................................
Date...16th. July, 1954...Members  (................................................

   (*687)   Wt. 11241--149   4,200   6/51   T.S.   839CONFIDENTIAL



The crash site south of the airfield.

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Notes:

On the web site there has been considerable speculation about the cause and investigation of this accident.   Comments have been put forward by Ron Gray, 4 Sqn Sabre pilot, who, with Snowy Ewens another 4 Sqn Sabre pilot, witnessed the accident from the top of the 4 Sqn Hangar tower; Eric Pigdon, 93 Sqn Sabre pilot who happened to be talking to Flt Lt Lind about station basket ball in the entrance to the runway and Homer caravan, who saw some of the accident and, by co-incidence, George Englefield-Bishop who was a corporal in the same Homer vehicle who witnessed the crash from the same rear doors of the caravan, but did not know Eric Pigdon at the time.   Finally, Ken Senar, 93 Sqn Sabre pilot who was Flying Wing Adjutant, who did not see the accident from his office but heard the crash.

One person thought he heard the engine stop before the aircraft nose-dived into the ground.   This appears not to be true as the AIB Inspector found that the engine was rotating at a high speed when it hit the ground.   Two others thought he forgot to retract his airbrakes in a low speed turn and flicked in.

I hope the publication of this report has cleared up these discrepancies although it still does not explain why none of the above witnesses were ever called by the Board of Enquiry.

[Click to see 4 Sqn F540 Report.]

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The report in Colin Cummings book on RAF Accidents "Category Five" says: " 08-Jul-54 XB647 Sabre F4 4 Sqn 3 miles south south west of Jever 1 killed.   After overshooting from a controlled descent, the aircraft executed a climbing turn to port at low speed, with the undercarriage retracted and the dive brakes out to a height of about 2000 feet, whilst turning through 90 degrees.   It then seemed to flick rapidly and to roll and lose height until it struck the ground.   The most probable cause was the loss of control at low speed and the failure to retract the dive brakes.   Flying Officer John JACK aged 24."