Was it serviceable?
VSF
Shy Torque has pointed out the purpose of this thread and I agree with him and indeed some of your comments since any attempt to define the cause of this accident is impossible - but then you don't find people guilty of Gross Negligence on this basis either. In the search for the truth that you claim to have found, you state that the aircraft was not found to be unserviceable prior to the crash - it was, of course not proven to be seviceable either - read the full AAIB conclusions. Of course if the BOI does not get given all of the relevant evidence relating to serviceability, aka in this case airworthiness, they may not look as widely as you might expect them to. We have not yet seen any evidence that this letter was shown to them, the Sherriff's FAI, or the other committees that have investigated this tragic accident - indeed I sometimes wonder if even the Reviewing Officers knew of its existence. This input from the Flight Clearance Authority is hardly grasping at straws - did you include it in your search for the truth? The bits in bold are my input.
File Ref: ADD/308/04 dated 6 June 1994
CHINOOK MC MK 2 - CA RELEASE TRIALS References:
A. A&AEE Letter Report TM 2210 - Chinook HC Mk 2 - Interim CA Release Recommendations.
1. You will be aware that at Reference A we were unable to recommend CA Release for the Chinook HC Mk 2 aircraft due to unquantifiable risks associated with the unverifiable nature of the FADEC software. However, we offered advice and proposed limitations aimed at minimising any risk associated with unpredictable FADEC software behaviour in the event that it became operationally necessary to use the aircraft prior to verified software becoming available. This advice assumed that the reliability and integrity of the hardware in the engine control system was adequate, as appeared to be the case from rig, bench, Service experience and integrity studies.
2. Since the introduction of the HC Mk 2 into Service in Oct 93, we are aware of at least 15 engine related incidents in a total of 1258 flying hours; this excludes those incidents that occurred during tests associated with the overspeed limiter checks. Of the 15 incidents, 4 are- considered to have particularly serious implications and are discussed below:
a. RAF Odiham Incident Signal DTG 081730Z MAR 94. ZA 704 - No 2 Engine flamed out after FADEC Reversionary Switch selected during pre-flight checks on the ground. No fault found.
b. RAF Odiham Incident Signal DTG 281232Z AFR 94. ZA 681 - No 1 Engine rapidly shut down after FADEC Reversionary Switch selected during pre-flight checks on the ground. No fault found.
c. RAF Laarbruch Incident signal DTG 1309232 MAY 94. ZA 671 – Nr rose rapidly to exceed 120% after both FADEC Reversionary Switches were selected during pre-flight checks. No fault found, but forward and aft rotor head tie bars were found to be distorted, indicating that the overspeed limiter system had failed to function.
d. RAF Odiham Incident Signal DTG 191545Z MAY 94. ZD 576 Emergency Power Caption illuminated twice in flight and once on the ground. PDT of No 1 Engine reached 950°C. No fault found, but blueing and minor cracking evident on blade tips of turbine nozzle assembly stators.
3. Three of the above incidents occurred on the ground during FADEC Reversionary lane checks, and there is in place a restriction on the manual selection of Reversionary mode in flight. However, we no longer consider this to be an adequate safeguard against the possibility of a potentially serious in-flight incident. The Reversionary mode is a vital safety feature in a full authority digital system and as such has to perform in a reliable and effective manner. At some stage we must expect a primary lane failure in flight which will result in the automatic selection of "Reversionary Mode" but experience to date suggests that the basic requisites of that system may not be met.
4. Whilst we are aware of the very considerable steps you are taking to determine the causes of these incidents and of the ongoing investigations involving a report from HSDE, the Textron 'White Paper', the EDS Scicon verification study and the T55 software block change proposals, I have to state that the serious, frequent and unexplained incidents to which I have alluded, have eroded what confidence we had in the Chinook HC Mk 2 engine management system. This unease has grown despite our meeting on 25 May. The unquantifiable risks identified at the Interim CA Release stage may not in themselves have changed but some have become more clearly defined by events, to an extent where we now consider the consequences of the risks and the probability of an occurrence to be unacceptable.
5. As a result of our concerns for the flight safety of the aircraft, I have regretfully taken the decision to suspend Chinook HC Mk 2 flight trials until such time as we are satisfied with the explanations for, and solutions to, the above incidents. Furthermore, we strongly recommend that you make our concerns known to the RAF in order that they may consider their, own position.
6. Please be assured that this decision has been taken in complete isolation from the tragic accident that occurred on the Mull of Kintyre on 2 June, and that we remain committed to pursuing the outstanding CA Release trials as soon as our flight safety concerns are overcome. In the meantime, we will of course continue to provide you with whatever advice and assistance we can in your deliberations and to help bring the outstanding investigations and studies to a satisfactory conclusion.
JB