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Aviation History
1925
1925 - 0083.PDF
FEBRUARY 12, 1925 THE CROYDON ACCIDENT Official Report Following is the text of the official report of the Court appointed to investigate the accident to the aeroplane G-EBBX, which crashed at Croydon on December 24. The Report is signed by Sir Arthur Colefax, K.C., Professor B. Melvill Jones, A.F.C., Mond Professor of Aeronautical Engineering at Cambridge University, and Mr. J. Swinburne, M.Inst.C.E., F.R.S. :— I have the honour to submit my report of the formal investigation whichyou appointed me to hold of the accident which occurred on December 24, 1924, at or near Croydon, Surrey, to the aircraft G-EBBX. Prof. B. MelvillJones, A.F.C., and Mr. J. Swinburne, M.Inst.C.E., F.R.S., who were appointed by you to act as assessors for the purpose of such formal investigation signthe report. The accident occurred shortly after noon on December 24 last, withina few minutes of leaving the aerodrome at Croydon, and resulted in the ss of the lives of all the passengers, seven in number, and of the pilot,a pt. D. A. Stewart, and the destruction of the aircraft. The certificate of registration, No. 1082, dated June 10, 1924, describesthe aircraft as an 11-seater biplane of the type D.H.34, having one engine, a Napier " Lion." The De Havilland Aircraft Co., Ltd., were the constructors,and Imperial Airways, Ltd., the owners of the aircraft. The certificate of airworthiness, numbered 587, and dated November 18,1924, gives as the power of the engine at ground level 440 h.p. at 2,000 r.p.m. The maximum total weight, including all items uf load, authorised by suchcertificate, is 7,20(1 lbs., out of which the tare weight is 4,674 lbs., and the load with full tanks (freight, passengers, goods, etc.i. 1,376 lbs. In November, 1924, between the 7th and the 15th, for the purpose ofobtaining a renewal of the airworthiness certificate, the machine was dismantled, the component parts examined, and with necessary replace-ments, again assembled, the work being carried out under the inspection of the Aeronautical Inspection Directorate. As is usual where a machinehas been dismantled, the inspection included a petrol flow test. The aforesaid certificate of airworthiness was issued on the recommendationmade on such inspection. Prior to its issue a flight test was carried out by the owners, as is usual on such an occasion, although the directions issuedpursuant to the Air Navigation (Consolidation) Order. 1923. do not require this to be done. Between the date of the certificate of airworthiness and December ISthe aircraft was in frequent use. carrying passengers and freight, and the maximum authorised weight was approached very closely on more thanone occasion. Its performance was satisfactory. On December 18 the aircraft with Mr. W. G. R. Hinchliffe as pilot flewto Amsterdam in very good time. The record of the engine revolutions given by the tell-tale device, which was a new instrument supplied iu Octoberor November, was particularly good. On arrival at Amsterdam Mr. Hinch- liffe, however, reported to the flying mechanic employed there by ImperialAirways, Ltd., that the engine was rough and that the oil pressure had fluctuated. A refuelling inspection was carried out, special attention beingpaid to the oil supply, and the aircraft left for Croydou, but returned to Amsterdam after about an hour's flight, the pilot again reporting low oilpressure and a rough engine. The oil filters were emptied and washed. a subordinate observing, as he lwlieved. although this was not otherwiseconfirmed, some white metal. In this he was probably mislead by the appearance of air bubbles in the oil filter. A test flight was then made,the mechanic, who at one time had been an officer pilot in the Royal Flying Corps, going up with Mr. Hinchliffc. Except for a little roughness—which,in the mechanic's view, was due to the gusty weather and to a possible slight fault on one or two of the plugs—he was satisfied. He, in fact, didfind later that two or three plugs were doubtful, and changed all the plugs. The oil pressure, he states was entirely normal; it dropped to approximately50 lbs. on the engine being throttled back, and increased perfectly normally and steadily when the throttle was opened again to full power. After thisflight test a practically full inspection of the engine and aircraft was carried through. On the 19th Mr. Hinchhffe started again for Croydon, but owingto bad weather combined with roughness of the engine, and fluctuating oil pressure, returned again after about an hour's flight. The mechanicagain made a thorough investigation, after which he reported the engine as fit to fly to Croydon. He formed the opinion that the low oil pressuresobserved were to be attributed to the oil congealing in the pipe leading to the indicator, and then contracting between the stoppage and the indicator.He had had experience of this before on another machine. The engine was giving its normal revolutions, although oil pressure as low as 25 lbs. wasreported by Mr. Hinchliffe as having been observed. A fog coming up, which rendered flying impossible, the mechanic again made a very detailedexamination of the oil system, and at all parts thereof obtained a satisfactory' oil flow. Further, he examined the castings for any possible cracks. Asthe fog continued and detained Mr. Hinchliffe at Amsterdam, the mechanic seized the opportunity of making w*hat he has described as a total inspection,which he did between December 20 and 23. The controls and cables were relubricated, the petrol system inspected, and the petrol pipes at the unionsimmediately adjoining the float chamber disconnected. Adopting the words of the mechanic in his evidence, no foreign matter was found, no foreignliquid, and on turning on the petrol at about If lbs. pressure a full-bore flow from each of the petrol pipes at the joint next the float chambers wasobtained. He ran the engine up on the 22nd and also on the 23rd. and was perfectly satisfied. I have set forth at length the facts, as I find them, as to what happenedat Amsterdam, because the attempt and abandonment on two occasions of the return journey to Croydon, and the pilot's reasons for abandoningthese attempts, are matters which have been pressed against Imperial Airways, Ltd. Whether there really was any defect in the oil supply to the engineat any time, or whether some cause preventing the indicator showing the actual oil pressures is ihe true explanation of the pressures observed byMr. Hinchliffe, may be open to some doubt, but I lean strongly to the latter. On December 23 Mr. Hinchliffe flew with one passenger to Lympne, viaOstend. He broke the journey at Lympne because of the weather and darkness. In an hour's flight on the 24th he completed the journey toCroydon, arriving at the aerodrome there at 10.30 a.m. He then wrote out his report, in which he described the engine as very rough and statedthat the oil pressure was " undulating low," but that for the last 60 minutes— presumably the time of the flight from Lympne to Croydon—it had notdropped below 58 lbs. The tell-tale record of the revolutions of the engine, referred to above, includes all the journey from Amsterdam to Croydon, butfor the last half-hour cf the flight from Lympne to Croydon it can no longer be read. This is not due to deliberate erasure, but has been caused by thisportion having been exposed to considerable riction in the handling which the chart has had. It is not an infrequent occurrence for a pilot to describean engine as rough. It is vibration which he notices, but this does not point to any particular defect, or indeed necessarily to any defect, in the engine,but may arise from other causes, as, for instance, any want of balance in the propeller. Mr. Hinchliffe landed at Ostend for petrol and oil. He statedin his evidence that he left Amsterdam in a gale, and that the time taken to Ostend was extremely long, the longest he had ever taken. The time of theflight v/as thus prolonged, doubtless by reason of the wind being adverse. The oil undulations, to use his own words, were slight but nothing serious,just as in his flight out from Croydon to Amsterdam, and the power of the engine was excellent. Still quoting from his evidence, the oil indicatorwas undulating, fluctuating slightly, but only as on his journey from Croydon to Amsterdam, and did not drop below 58, which was quite a normal reading.Such fluctuations in the indicated oil pressure as were observed in conjunc- tion with the roughness he noticed in the engine—the two together—tended,he said, to make him a little more careful. With regard to the flight from Ostend to Lympne, he gave it in evidence that the power of the engine wasexcellent and that the fluctuations in the oil pressure indicated were just as before : and with regard to the flight from Lympne to Croydon on the24th, that the engine was just the same as it had been from Amsterdam to Ostend, and from Ostend to Lympne, and that the oscillations of the oilindicator still continued, not dropping below 58. With these facts in mind, Mr. Hinchliffe wrote out the report to which I have already referred. Beforedoing so he reported to Mr. Stirling, the foreman of day maintenance, in the presence of Maj. Brackley, the air superintendent of Imperial Airways,Ltd., that the engine was rough and that the oil pressures had fluctuated. After writing out the report he also spoke to the mechanical superintendent,Mr. Hall, telling him of the roughness of the engine and the fluctuations in the oil pressures indicated. The tell-tale record for the flight from Amsterdamhas been carefully examined by witnesses who have been called before me, and on their evidence 1 find that not only is nothing indicated as wrong withthe engine, but that, looked at as a whole, it shows that the engine behaved remarkably well. At Croydon on the morning of December 24, after the aircraft was handedover by Mr. Hinchliffe, Mr. Stirling opened the throttle fully and found the revolutions to be 1,875. He switched off one magneto and then the other totest the plugs, and found them to be in order. He took notice at all speeds at which the engine was running whether there was any undue vibration,without detecting any. The oil pressure he found to be 60 lbs. His conclusion was that the engine was " splendidly built and in good condition." Inaddition to the re-fuelling inspection, the oil tank was examined to see whether any trace of white metal could be found, but none was found. This re-fuellinginspection, as also the examination of the oil tank, was done under the super- vision of Mr. Clark, who also holds a ground engineer's licence. He foundeverything was normal. He then started the engine and after warming up ran it at fully open throttle, trying each ignition switch. He then throttleddown slightly and shut off one petrol tank and opened the engine again to full throttle, afterwards making a similar test of the other petrol tank supply.Mr. Clark also examined the tell-tale record referred to above, the portion covering the last half-hour of the flight from Lympne to Croydon onDecember 24, being then readable. He attributed the roughness which Mr. Hinchlifie had reported to the atmospheric conditions of the flight to and fromAmsterdam, and it should be observed that there is no evidence of any rough- ness of the order which would result if any of the cylinders were not working,and also that no drop iu revolutions occurred which must have been the case if any of the cylinders failed to operate. He signed the daily certificate ofsafety of aircraft, such certificate in form complying with the requirements of the Air Navigation Directions, paragraph No. 37 (a), (6) and (c) of A.N.D. 3. In setting forth, as I have done, at length the facts as I find them whichrelate to the inspection of the aircraft at Croydon on December 24, I have had in mind the contentions as to negligence on the part of Imperial Airways, Ltd.,which have been urged before me. I am satisfied that every reasonable precaution was taken by Imperial Airways, Ltd., to prevent any detectabledefect in the engine being overlooked, and that Mr. Clark was fully justified in signing the daily certificate of safety of aircraft referred to above. I have given careful consideration to the question whether the circumstancesdemanded, as a matter of prudence, that a test flight should have been made before the flight with passengers was undertaken. It is difficult, if notimpossible, to imagine anything amiss with the engine, or its installation, or otherwise with the aircraft, which a test flight could have been expected toreveal which the flight from Amsterdam to Croydon had not afforded ample opportunity of revealing. In my judgment the facts as to that flight did notcall for more being done than that the ground test should be made, as I find it was. with careful attention to the two matters which Mr. Hinchliffe inwriting and otherwise had referred to. Ground tests satisfactorily established that there was nothing wrong with the lubrication, and confirmed Mr. Hinch-liffe's view that in the matter of power the engine was excellent. Accordingly, 1 find that a flight test was not called for, and that it was in no way negligentor imprudent to embark upon the flight with passengers without making such a test. I need say nothing about the circumstances in which a flight test isdeemed desirable, and is made, except that they did not exist in the present case. Before starting on December 24, Captain Stewart made his own examinationof the aircraft, ran the engine up to full throttle, and signed the pilot's certificate of general fitness of aircraft before flight. He had been toldpreviously by Mr. Hinchliffe of the latter's experience of the machine. He was both an experienced and skilful pilot, and no blame is attributable to him.On December 24. another machine, also loaded **o as to be within a few pounds of the maximum authorised total weight, with Captain Barnard aspilot, started from the Croydon aerodrome for Paris about a quarter of an hour after Captain Stewart had left. This machine was also a D.H. 34 type,and had a Napier " Lion " engine, similar in all respects to the engine of G-EBBX. When almost half a mile south of the fence which forms thesouthern boundary of the aerodrome, this machine came within 20 ft. of the ground. Captain Barnard, in his evidence, has said that he experienced aconsiderable down draught which came over the crest of the hill, which is about 8(1 ft. higher than the ground at the southern boundary of the aero-drome. He also stated that owing to the wetness of the ground his run along it was somewhat longer than usual, and that the down draught caused him tolose height between the fence and the place where he came so near to the ground. Captain Stewart's take-off was observed by several of the witness, of whomCaptain Barnard and Mr. Clark were not more than 25 yards to the west of the course of the take-off which was in a southerly direction. The run alongthe ground was unusually long, doubtless because of the wetness of the ground, although possibly intentionally prolonged in order to have a greater speedat the moment of leaving the ground. The machine passed about 25 ft. above the fence, which is about 6 to 7 ft. high. It was stated that the climb wasgood, and that the machine, at one time, was some 500 it. above the level at 83
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