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DETERMINATION 1

NOTE:
I	INTRODUCTION	10
II	THE LEGAL FRAMEWORK	10
III	THE EVIDENCE GENERALLY	19
IV	THE BACKGROUND TO THE ACCIDENT	22
V	THE FINAL FLIGHT OF ZD576	55
VI	THE AAIB INVESTIGATION/RACAL REPORT	63
VII	THE CAUSE OF THE ACCIDENT	73
VIII	TRAINING CONSIDERATIONS	106
IX	COCKPIT VOICE RECORDER AND ACCIDENT DATA RECORDER	115
X	MISCELLANEOUS MATTERS	119

PAISLEY, 21 MARCH 1996
[Sidenotes omitted editorially]

  The Sheriff, having resumed consideration of the evidence and submissions thereon, determines as follows:

  1.  Chinook MkII helicopter ZD576 was delivered to RAF Aldergrove on 31 May 1994. It had recently been the subject of a mid-life update by its manufacturers, Boeing Helicopters.

  2.  The operation of ZD576 was subject to the terms of the CA Release issued by the Controller Aircraft who is responsible to the Secretary of State for Defence. The CA Release, which may be amended from time to time, certifies the airworthiness of the type of aircraft to which it relates within the particular limitations set forth therein. At the material time ZD576 was subject to limitations in respect of weight and icing clearance.

  3.  On 2 June 1994 in the late afternoon ZD576 was tasked to carry a group of 26 passengers from RAF Aldergrove to Fort George near Inverness. In the event only 25 passengers went on the flight.

  4.  The crew of ZD576 for the flight to Fort George were Flt Lt Tapper (captain), Flt Lt Cook (co-pilot) and MALM Forbes and Sgt Hardie (crewmen).

  5.  Before departure of the flight the crew obtained from the Met Office at Belfast International Airport up-to-date terminal area forecasts and actual observations which covered their planned route to Fort George. The forecast for the Machrihanish area was that visibility in general would be 7,000 metres in haze with the scattered cloud base at 1,200 feet and the broken cloud base at 3,000 feet and that temporarily between 1400 and 2100GMT the visibility would be 4,000 metres with the broken cloud base at 500 feet. In addition there was a 30 per cent probability that between these times the visibility would be reduced to 500 metres in fog with the broken cloud base at 100 feet. The actual observations taken at Machrihanish at 1416GMT indicated that the visibility was 4,800 metres in haze with the scattered cloud base at 200 feet and the broken cloud base at 800 feet.

  6.  The journey to Fort George was planned by the crew to be flown under Visual Flight Rules (VFR) at low level on the way out and at medium level on the return to RAF Aldergrove.

  7.  Before departure the crew left with an operations clerk at RAF Aldergrove copies of three sections of a 1:500000 scale map on which had been recorded details of the planned route to Fort George including tracks, distances, estimated times and safety altitudes for each leg of the sortie.

  8.  The planned route was to fly from RAF Aldergrove to the lighthouse at the Mull of Kintyre, thence to Corran near Fort William and thence up the Great Glen to Inverness and Fort George. On the first leg to the lighthouse the track was shown as 027ºM, the distance 42 nautical miles (nm), the time 21 minutes and the safety altitude 2,800 feet.

  9.  During pre-flight procedures, the crew entered five waypoints into the aircraft's RNS252 SuperTANS computer. Waypoint A was entered as N55º 18.50 W005º 48.00 which was a point approximately 280 metres south east of the Mull of Kintyre lighthouse. Waypoint B was entered as a point near Corran.

  10.  In due course the 25 passengers boarded the aircraft and at 1642GMT (1742BST) a member of the crew reported to Aerodrome Control at Belfast International Airport that the aircraft was lifting and departing.

  11.  At 1643GMT a member of the crew reported to Approach Control at the airport that the aircraft was outbound on a course of 027ºM at low level. At 1646:14.06 a further report was received from the aircraft to the effect that it was at the airport zone boundary (approximately 9nm from the airport) flying VFR. These reports were all routine and unexceptional.

  12.  During the flight Flt Lt Tapper occupied the left hand seat in the cockpit of the aircraft and acted as non-handling pilot while Flt Lt Cook occupied the right hand seat and acted as handling pilot. MALM Forbes acted as No 2 crewman at the front of the cabin while Sgt Hardie acted as No 1 crewman at the rear.

  13.  At about 1750BST the aircraft was observed flying at low level over Carnlough on the Antrim coast and out over the North Channel in the direction of the Mull of Kintyre.

  14.  At 1655:14GMT a member of the crew called the Scottish Air Traffic Control Centre (Military) at Prestwick in the following terms: "Scottish Military, good afternoon, this is F4J40" (which was the aircraft's callsign). This was not an emergency call. For reasons which are not known the call was not answered. Nor was it repeated. No further radio communications were heard from the aircraft.

  15.  At the time or shortly after this call was made the aircraft was observed flying below the cloud base at a height between 200 and 400 feet and at a point about 2nm south west of the Mull of Kintyre lighthouse. It was in straight and level flight and heading in the direction of the land mass of the Mull at a steady speed.

  16.  At this time cloud and hill fog extended over the land mass from approximately the base of the lighthouse building (at 250 feet above sea level) to at least the summit of Beinn na Lice (1404 feet) which is situated a little under 1nm east of the lighthouse.

  17.  When the aircraft was about 0.81nm from the position entered into the SuperTANS for the lighthouse (waypoint A) on a bearing of 018ºT a member of the crew manually changed the waypoint displayed on the SuperTANS (which was in Tactical Steering mode) so as to give steering, distance and time to go information to Corran (waypoint B).

  18.  This change of waypoint was made when the aircraft was approximately 400 to 500 feet above sea level.

  19.  After the change of waypoint the aircraft flew towards the land mass of the Mull on an ascending track of 022ºT (which was approximately two degrees to the right of the track which the crew had planned to follow from RAF Aldergrove to the lighthouse and nine degrees to the right of the planned track from the lighthouse to Corran).

  20.  A few seconds after the change of waypoint (and about 15 to 18 seconds prior to impact with the land mass of the Mull) the aircraft was at a height of 468 plus or minus 50 feet above sea level.

  21.  At some stage the aircraft entered Instrument Meteorological Conditions (IMC). This required the aircraft to transfer to flight under Instrument Flight Rules (IFR), and in particular to climb at least as high as the calculated safety altitude for that leg of the route, namely 2,800 feet.

  22.  At a point in time some 2.9 seconds before the initial impact, the aircraft was climbing at a rate of approximately 1,000 feet per minute and at an airspeed of approximately 150 knots. To this speed there fell to be added a tailwind component of approximately 24 knots which resulted in a groundspeed of approximately 174 knots.

  23.  At that point in time large aft and left cyclic and collective control inputs were made in the aircraft which resulted in a final cyclic flare before the aircraft struck the ground. During this final flare the aircraft travelled approximately 812 feet over the ground, increased its rate of climb to approximately 4,670 feet per minute and climbed approximately 128 feet. In addition the flight path angle increased to 20º above the horizontal and the nose of the aircraft was pitched up to about 31º above the horizontal.

  24.  The distance between the point where the change of waypoint was made and the initial impact point was about 0.95nm.

  25.  The aircraft initially struck a rocky outcrop on the side of Beinn na Lice at a point 810 feet above mean sea level and approximately 0.28nm east of the Mull of Kintyre lighthouse.

  26.  At the time of the initial impact the aircraft was travelling at a groundspeed of approximately 150 knots on a track of approximately 012ºT. It was banked some 5 to 10º to the left with a yaw angle of less than 10º.

  27.  Upon initial impact much of the fuselage undersurface of the aircraft and rear end was torn off and the right and lower area of the cockpit damaged.

  28.  The aircraft then travelled almost 200 metres airborne while sustaining fuselage strikes from rotor blades and executing extreme violent manoeuvres. It impacted the ground inverted and broke into two major pieces which tumbled a short distance, shedding the aft pylon and both engines. Fuel tanks on both sides were ruptured at initial impact and extensive ground fire initiated, severely damaging much of the remains.

  29.  The time of the initial impact was approximately 1759:30BST on 2 June 1994. All the occupants of the aircraft were rendered unconscious at once and died more or less instantaneously.

  30.  The names of those who died, and the cause of death in each case, were as follows:

  31.  The wreckage of the aircraft was subsequently examined in very considerable detail by Mr Cable, a Senior Inspector of Air Accidents (Engineering) with the Air Accidents Investigation Branch (AAIB) of the UK Department of Transport, assisted by various colleagues and other personnel from Boeing Helicopters, a number of component manufacturers and the RAF.

  32.  Fire damage to the wreckage of the aircraft was consistent with the effects of the accident. No evidence of explosive effects or pre-impact fire were found.

  33.  The completeness of the aircraft at impact could not be positively verified but no evidence was found to suggest pre-impact separation of any part.

  34.  The groundspeed and drift indicator of the aircraft was probably registering 147 knots groundspeed at, or very shortly after, the initial impact.

  35.  Engine condition and the available evidence of instrument indications and control settings in the aircraft suggested normal operation of both engines at the time of the accident.

  36.  Fire damage prevented assessment of the functionality of No.1 DECU and had destroyed its memories of the operating program and exceedance and fault history.

  37.  The No.2 DECU remained partially functionable, with deficiencies that were consistent with the effects of impact damage.

  38. The No.2 DECU memories showed that the operating program and constants had not altered since delivery, that no abnormal exceedances or faults had been detected over its life and that no faults had been detected on the last flight.

  39.  HMA internal settings confirmed correct operation for most HMA elements and indicated power levels that possibly reflected aircraft manoeuvre effects.

  40.  Thorough assessment of most flight control hydraulic system components of the aircraft was possible and revealed no signs of pre-impact failure or malfunction. Available cockpit indications indicated that both systems were providing normal pressure at impact.

  41.  Available evidence indicated normal AFCS operation.

  42.  Available evidence precluded major pre-impact loss of electrical supplies but indicated that all electrical systems had probably de-energised almost immediately on initial impact.

  43.  No signs of pre-impact malfunction of the transmission or rotor systems were found.

  44.  Almost all parts of the flight control mechanical systems of the aircraft were identified, with no evidence of pre-impact failure or malfunction, although the possibility of control system jam could not be positively dismissed.

  45.  Most attachment inserts on both flight control system pallets had detached, including the collective balance spring bracket that had previously detached from the aircraft's thrust/yaw pallet, with little evidence available to eliminate the possibility of pre-impact detachment.

  46.  The method of attaching components to the pallets appeared less positive and less verifiable than would normally be expected for a flight control system application.

  47.  The aircraft's radar altimeter receiver was excessively sensitive, probably a pre-existing condition that was mainly the result of incorrect adjustment. The fault had the potential for causing erroneous height indication but a previous flight test result indicated that this was unlikely, provided the antenna environment for the aircraft was similar to that for the test.

  48.  The radar altimeter receiver's excessive sensitivity would have increased the maximum indicated height error build-up in circumstances where the terrain closure rate exceeded the system's tracking capability.

  49.  A detailed investigation of possibly relevant technical aspects of the accidents was made. The pre-impact serviceability of the aircraft could not be positively verified but no evidence was found of malfunction that could have contributed to the accident, with the possible exception of the radar altimeter system fault.

  50.  The aircraft was not fitted with either a cockpit voice recorder or an accident data recorder. Had these been fitted it is likely that they would have led to the recovery of important evidence relevant to the circumstances of the deaths and, more particularly, the cause of the accident.