Waypont
Walter Kennedy
In reality nobody knows exactly where the WP change took place as the method of analysis of where it might have taken place depended on the critical assumption of aircraft speed working back from the impact point and the “ingenious and complicated” method employed to analyse the TANS data – an analysis where the TANS manufacturer Racal did issue a “health warning”. It was also a bedrock of this analysis that the aircraft had been serviceable and fully under the pilots’ control throughout. However the HofL hearing try to paint a “fair picture” stated as follows:
HofL Part 3
53. The aircraft was fitted with a Racal Avionics "SuperTANS" Tactical Area Navigation System providing navigation information from two independent sources. The system enables a number of way points to be fed into it before a flight. When flying from the point of departure to the first way point the screen[20] shows bearing, distance and "time to go" from the aircraft's current position to the way point. When the pilot alters the system from the first way point to the second, the distance and bearing of the former are replaced on the screen by those of the latter and so on as way points are progressively changed. Racal confirmed that the system was performing perfectly at the time of loss of power and extracted from its memory the information that way point B had been selected when way point A was 0.81 nautical miles distant, bearing 018°. The distance from the way point change to the point of impact was 0.95 nautical miles. The system gave no information as to height or time at the way point change but had recorded that at approximately 15-18 seconds before power down the aircraft was at a height of 468 feet ± 50 feet (Board report para 49). The manufacturers have told us that "18 seconds is likely to be a better estimate".[21] The TANS had also recorded that the height above sea level at impact was 665 ft[22], whereas in fact it was 810 ft. The investigating board noted this discrepancy (para 49); they considered it probably due to "the mechanics of the crash and the developing fireball", but we know of no evidence to support this. The TANS is not intended to act as a Flight Recorder or what is colloquially known as a Black Box, and the information referred to above was achieved by a somewhat complicated and ingenious method of extraction employed by Racal.
As you can see there is considerable doubt as to whether the height recorded at the WP change would have been accurate, but more importantly I understand that because the TANS does not have an external time reference the timing estimates taken from the system had to assume aircraft speed based on the assumption, albeit an informed one, of impact speed. Thus in terms of time and distance to the WP there is a danger of a circular hypothesis developing. Racal made it clear that the methods used to extract data from the TANS were certainly not equivalent to a forensic recorder such as an ADR, and hence the TANS information gives estimates thus adding to hypotheses not facts. However two questions, please, for those SH pilots out there:
If we accept the TANS data as correct is 0.81NM, even with a GS of around 150kts (an assumption still based on TANS data – not a fact), an unusually close (or even dangerously close) distance to turn 7 degrees left in VFR conditions?
Why does everyone assume that the aircraft was “serviceable” at the time of the waypoint change? If an emergency was developing, or indeed had developed, such that you had lost control of the aircraft or engines in some way would it not be quite reasonable for MALM Forbes in the middle seat to have selected the next waypoint as the safe heading to fly?
I am not saying this happened, but so far all of the operational scenarios seem to have been predicated on the pilots being guilty of gross negligence – how about you operators trying a few that would be based on their innocence! Remember even the Board started with the totally unsubstantiated (in terms of what they then found) statement that “Nevertheless, there was sufficient evidence to eliminate as possible causes: major technical malfunction or structural failure of the aircraft prior to impact; …… Therefore the Inquiry focused on the crew’s handling and operation of the aircraft.” But even then they did not find any totally conclusive proof of pilot error (a balance of probabilities is just what it says it is – and we must remember the pressure they would have been under the second time round) let alone negligence – just about all of their conclusions are hypotheses – later turned to “facts” by the Reviewing Officers. The central question that the Board does not seem to have considered at all, is whether, either as a result of the Release to Service process and/or the defect history of the aircraft, the “airworthiness chain” was still intact for ZD576. As any of you who have read my full report on the Chinook web site will know in my view there is clear evidence that it was not.
FJJP’s last post sums it up nicely, but while MOD continues to maintain this grossly unjust and criminal smear of “culpable homicide” against the pilot’s names we have to continue the fight. Nobody will ever know the cause of this accident, but we all know where the real issues lay then as now, and I suggest that eventually MOD may be more permanently embarrassed by what we are finding as we are able to dig deeper into the background to this accident, the problems with the introduction to service of the Chinook Mk2 and the inconsistent nature of RAF justice at the time, than they would be in the short term by any withdrawal of the Gross Negligence verdict.