Reply to thread

Message: <blockquote data-quote="straitman" data-source="post: 2150065" data-attributes="member: 3635">Wreckage site examination There was some intermingling of the wreckage of Lead and No 2 on the surface of their respective craters. Positive identification was established from identifiable components such as brake 'Maxaret' units which were deeply buried in the crater. The individual aircraft flight paths at the time of impact were determined by compass sightings taken through the clearly obvious centre-line of each impact crater. In comparing the individual flight paths and impact points at the moment of the crash, and in relating this comparison to the fatal manoeuvre, the following deductions were made:<ul> <li data-xf-list-type="ul">No 3, being on the high side had appreciated the dangerous proximity of the ground during the final stage of the roll. He had broken formation, levelled his wings, and had made every effort to pull up before striking the ground. </li> <li data-xf-list-type="ul">No 4 had also appreciated the dangerous situation and had taken similar action to that of No 3, but slightly later. It is possible that the sudden movement of No 3 prompted the action of No 4. The slope of the ground, when related to the flight path of No 4 immediately prior to impact, was such that with wings-level his left wing could have struck the ground first. </li> <li data-xf-list-type="ul">No 2 had an impact flight path truly parallel with that of No 4. The position of No 2 in the formation was such that in the final stage of the roll he was looking up at the leader and would not have appreciated the proximity of the ground. </li> <li data-xf-list-type="ul">Lead had an impact flight path which was 10° to the right of the parallel impact flight paths of No 2 and No 4.</li> </ul>All the damage to the airframe structures of the four aircraft was consistent with the aircraft striking the ground at high speed. In every case the control surfaces were either still attached to the main surfaces or had been torn from the hinge points, as could be expected from the broken-up condition of the wreckage. There was no evidence to suggest that any control surface has failed or become detached in flight. Broken control cables had failed with the characteristic fraying associated with grossly excessive tension loads. No evidence was found to suggest there had been a midair collision or birdstrike.The lead aircraft had struck the ground right wing low in a nosedown attitude. The outer portion of the right mainplane had broken off relatively intact. The aircraft had then overturned as was evidenced by the turf marks on the top surface of the port mainplane and the ruptured condition of the booms. No 2 aircraft had impacted in a level attitude but at a high rate of descent. The plan form of the aircraft was plainly visible in the soft ground. The fuel tanks had also burst and the fuel had ignited. No 3 aircraft was not nearly as broken up as were the three other aircraft. In fact, the instrument panel of this aircraft was found relatively intact. The damage sustained on impact was consistent with a high speed but low rate of descent.No 4 aircraft had struck the ground in a tail-down attitude. The skin of the underside of the left mainplane had virtually disappeared but portion of the upper surface skin of this mainplane had burst from its securing rivets and was quite bright and clean. Much of the right mainplane undersurface was still attached, and the top surface was distorted by an explosion inside the mainplane. The aircraft must also have had a high rate of descent.The turbine discs of Lead, No 2 and No 4 aircraft became detached from the engines and it was evident from the condition of the turbine blades that these engines were under power at the time of impact. The turbine disc of No 3 aircraft was still attached to the shaft of the engine, due to the lesser rate of descent of this aircraft. The turbine wheel had dissipated its inertia by grinding away the nozzle guide vanes of the engine. Here again it was evident that the engine had been under power at the time of impact. Virtually the only aircraft instrument that yielded information was the clock of No 3. This showed a trip duration of 25 minutes and had stopped at 1403 hrs.No evidence was found that would lead to the belief that any other item of equipment in the aircraft had in any way contributed to the accident.Discussion of the evidence Formation flying requires great concentration on control and positioning. It is essential that all formation members rely implicitly on the leader for altitude, attitude and safety considerations. They concentrate solely on precision positioning. It follows that an explanation as to why the leader allowed a hazardous situation to develop will account for all aircraft crashing. No 3 attempted individual recovery at a very late stage despite the prerogative of the leader to carry out this action for all. This fact in itself indicates there may have been something wrong with the leader or lead aircraft, as the formation leader should have had the best appreciation of the situation.Investigation determined that all engines were under power at the time of impact. Further, had power failure occurred in the lead aircraft the formation would have lost its identity immediately, and at a height sufficient to enable breakaway action to be taken. The leader would not have aggravated the situation by adopting such a flight profile. There was no evidence to suggest that an unserviceability of engine, airframe, or other equipment was the direct or indirect cause of the accident.It was considered possible the leader could have encountered control loss due to foreign object jamming. During recovery from a barrel roll, increasing back pressure is required on the control column. This is particularly so as the angle of bank reduces to around about 20°-30°. Thus, any restriction which did not occur before this required amount of back stick was needed would not have been evident to the pilot before this stage of the roll was reached. A pilot confronted with this situation at 600-700 ft would most probably resort to 'pulling hard'. The natural tendency would be to use both hands on the control column. In such circumstances it would be foreign to remove one hand to use the R/T button on the throttle lever. Also, in such a situation the manoeuvre would follow a flight path closely akin to the last stages of a normal barrel roll. The aircraft would be decreasing its angle of dive, which would give the other members of the formation the impression that recovery was fairly normal. Too low a height would be their first indication of trouble and this when it was too late. This is probably the only type of difficulty which could thus confuse them. From examination of the wreckage it was quite impossible to determine whether such a restriction had occurred.As leader, a pilot would continually cross-reference on his ASI and altimeter. An erroneous indication either by an altimeter malfunction or misreading could influence his key positioning. This would not, however, override his visual observations and orientation, and action could have been taken to initiate a more positive recovery. A midair collision immediately prior to the aircraft striking the ground could have been a possible cause; however, it could only have occurred at a very late stage of the roll and in such a manner that it was not observed by the witnesses who watched the aircraft complete an aerobatic manoeuvre and dive into the ground.The possibility that No 3 may have collided with the leader is not borne out by the observations of witnesses. Although No 3 was observed to break from the formation, this was due to his appreciation of the impending impact. Lack of visibility on the part of the leader might have been a contributory factor. However, no substantial evidence to this effect was determined. While the final track of the formation was into the sun, the aircraft were on a downward path at the conclusion of the barrel roll. The angle of elevation of the sun at that time of day on the 15th August 1962 was 30° above the horizon; therefore, dazzle from the sun was not considered to have been a direct cause.Close attention was given to the medical aspects of the investigation, particularly in the case of the formation leader. The fact that Lead had been subject to a medical board arising from an incident in Malaya was well known to many flying personnel at the time. This was the subject of a considerable amount of inaccurate gossip as soon as the accident became known, the reference being to 'blackouts' which Lead was said to have experienced. The medical conclusion was that there was no evidence of physical disability on the part of the formation leader contributing to the accident.The final manoeuvre A loose barrel roll is a very simple manoeuvre to carry out. The leader may have allowed the nose of his aircraft to drop to such a degree that recovery from the resultant dive was impossible. The accepted objective in a barrel roll is to produce a helical flight path through 360° in the rolling plane and encircling a pre-selected point directly ahead of the line of flight. The selected point is normally on or slightly above the horizon. Ideally the flight path should describe identical symmetrical arcs above and below the horizontal level of the selected point.To achieve this objective, one of the two following basic techniques is usually employed:<ol> <li data-xf-list-type="ol">Entry to the manoeuvre is from a shallow dive directly towards the selected point and a turn of approximately 30° away from this point, in the opposite direction of the barrel roll. The nose is then raised and rolled, aiming to keep the 30° angle off from the selected point constant throughout the helical circumference of the roll.</li> <li data-xf-list-type="ol">Entry to the manoeuvre is from a shallow dive with wings level and on a flight path positioned to one side of the selected point, giving an angle off of 30° from this point. The nose is then raised to 30 above the selected point and rolled, aiming to keep the 30° angle-off constant throughout the helical circumference of the roll.</li> </ol>There are many variable factors which govern the flight profile during a barrel roll. The more important ones, each of which is variable, and all of which are controlled by pilot technique, are:<ul> <li data-xf-list-type="ul">the maximum nose-up flight angle achieved during the first half of the manoeuvre; </li> <li data-xf-list-type="ul">the average rate of roll during the first half of the manoeuvre; </li> <li data-xf-list-type="ul">elevator control technique approaching and passing through the inverted stage; </li> <li data-xf-list-type="ul">the average rate of roll during the second half of the manoeuvre; </li> <li data-xf-list-type="ul">elevator control technique during the latter half of the manoeuvre; </li> <li data-xf-list-type="ul">the initial entry speed; and </li> <li data-xf-list-type="ul">engine power setting used.</li> </ul>In the case of a sequence of aerobatics, the aircraft may commence a barrel roll from level flight at the conclusion of a previous manoeuvre, because adequate speed has already been acquired and the aircraft is at the minimum specified altitude. Had the formation leader intended to perform a barrel roll about a horizontal axis, an error of judgment or faulty technique could have resulted in an excessive loss of height. If it were being performed a very low altitude, then the safety margin would be reduced accordingly. In this instance the difficulty of recovering a formation from such a situation must be considered, especially as regards restricted manoeuvrability.Contributory factors Either or both of the following factors could have been an underlying cause of the accident:<ol> <li data-xf-list-type="ol">The accepted practice of observing a minimum height of 500 ft for formation team aerobatic manoeuvres. It is apparent that the Red Sales were in the habit of executing formation aerobatic manoeuvres down to the minimum briefed height of 500 ft. If the formation had initiated their final barrel roll at a height of 1 000 ft, the accident would not have occurred. </li> <li data-xf-list-type="ol">Insufficient regular practice by the leader in performing the team aerobatic routine at low level. It is significant that subsequent to flying a total of four dual sorties and one solo lead sortie during practice sessions by the Red Sales, prior to the departure of the previous leader of the team, the leader had led the team on only four occasions, which were spread over a period of eight weeks.</li> </ol>Conclusion Due to the very nature of this accident and the degree of aircraft breakup, post-impact examination achieved only limited results in some aspects. Consequently, there was insufficient evidence to isolate with certainty anyone underlying cause. It was established that the accident to the formation resulted from failure of the leader to carry out timely recovery action when committed to a low-level aerobatic manoeuvre. Whilst the cause of the accident will never be positively known and certain speculation must always exist, credence must be given to the following three possibilities:<ul> <li data-xf-list-type="ul">An error of judgment or faulty technique on the part of the leader in executing a barrel roll to the left at low level. </li> <li data-xf-list-type="ul">Foreign object restriction of elevator control movement. </li> <li data-xf-list-type="ul">Physical disability affecting the leader.</li> </ul>However, the weight of evidence indicated that the accident occurred as a result of an error of judgment, or faulty technique on the part of the leader.</blockquote>

Verification