ACCIDENTS_INVESTIGATION_BRANCH.

 

Precis_of_Investigation_No._W.1725.

 

 

Brief Description.

 

The pilot was engaged on a practice cross-country flight over a route as follows: Base, Northampton, Melton Mowbray, Fakenham, Stowmarket, Savernake, Northampton, Bombing Range, Base. Earlier the same evening this exercise had been successfully completed by flight Sergeant Merridew accompanied by a screened pilot whom he had satisfied as to his competence to repeat the practice together with his crew. The same aircraft was used after refuelling and an inter- flight inspection. The flight commenced at 0045 hrs and appears to have proceeded normally for one hour and fifteen minutes. The aircraft was then sound plotted by the R.O.C. post at N Elmham proceeding in a north-Easterly direction at an estimated height of 1,000 ft. Shortly after it had gone out of earshot there was a tremendous flash and the sound of the impact was heard. The only message from the aircraft during the flight was a position signalled at 0152 hrs, indicating it to be at 52.47 N, 00.17 E., which was in the vicinity of Sutton Bridge, 36 miles west of the scene of the accident. The R.O.C. plot then showed it to be flying at 8,000 ft.

 

Inspection at the scene of the accident indicated that a structural failure had occurred at a comparatively low altitude, but there was a trail of fabric extending for over 2,000 yards. The aircraft had stuck the ground at a very steep angle and was disintegrated and burnt by fire which occurred on impact.  There was no evidence to show any attempt had been made to abandon the aircraft.

 

A detailed examination of the parts which became detached in the air revealed the following :-

 

Mainplanes:  Both outer wings had failed in download, the port at station 20 and the starboard at station 16.

 

Fuselage: This had broken away at station 82 approximately and carried only major parts of fin and rudder, the top portions of which were found elsewhere. The tail turret had broken away separately.

 

Tailplanes: Both port and starboard had broken off in download at the attachments to the fuselage. The plans were lying less than 50 yards apart and almost stripped of fabric. The starboard tailplane still had the elevator attached: it was comparatively intact. The port elevator was in six separate pieces, the spar being broken at each hinge point. These six pieces were not very widely separated from each other or from the tailplane. The port tab was broken in two, opposite No. 2 elevator hinge; it had gone with the elevator. The old type jack (Pt. No.1399) was fitted to this side whereas the new type (Pt. 8352) was on the starboard elevator. It was noted that the starboard jack was free but that the port jack had gone to the limit of its travel and had stuck there. It is considered that this was due to the pulling of the control wires in the break-up. It was impossible to check the positions of the tabs from what remained of the pilot’s control.

 

Fabric: This was widely scattered and extended back for over 2,000 yards and was noteworthy for the number and smallness of the pieces. Examination showed that the fuselage fabric was among the earliest pieces but that tailplane pieces were also well distributed. The stringing had almost invariably parted leaving short ends in the fabric.

                                                                                                               

Weather Conditions.

 

Cloud 10/10ths with base at about 2,000 ft extending up to 8,000 ft. Visibility below cloud 12 miles. In the cloud there was high icing index and freezing level was given as 2,000ft. Wind N.N.E. 6 M.P.H. Bright moonlight outside cloud. It was observed by the R.O.C. witness at N. Elmham that a heavy hailstorm occurred two minutes after the accident.

 

Pilot’s History.

 

The pilot’s total flying time amounted to 556 hrs, much of which was done on target towing duties in single-engine aircraft. His experience on Wellingtons, dual and solo was 43 hrs by day and 19 hours by night. His instrument flying amounted to 6 hours solo and 64 hours total on the link trainer.

He was assessed as an “Average” pilot. There were two notifications of “carelessness” in his log book.

 

Aircraft History.

 

The aircraft was built by Vickers, Broughton works in October 1943 and had completed a total of 546.40 hours in the air, and 20.15 hours since the last minor inspection. Neither Mod. 1603 nor Mod.1883 had been incorporated but in this instance the absence of these did not cause the spar failure. There had been no recent repairs to the fabric or airframe.

 

Conclusions.

 

The accident was caused by loss of control which was followed by structural failure in the ensuing dive.  The primary cause of loss of control has not been established but probably occurred in cloud or icing conditions. It is known that Wellington aircraft become progressively nose heavy at high speed and that this tendency if not corrected will quickly lead to failure of the wings and tailplane under download conditions.

 

It is considered that the stripping of the fabric on the fuselage was the result of the stresses imposed in a high speed drive. The tailplane fabric probably became detached during the breakup.

 

The R.O.C. 1,000 ft plot of the aircraft just prior to the crash was by sound only and is considered unreliable.

 

C.I. (Accidents).                                                                              Unknown signature.

 

4/2/44.                                                                                              For C.I. (Accidents).

 

Distribution:  Bomber Command.

                       R.A.E.

                      A.M.File. No. G.38731/43.