Flight PA103 departed London-Heathrow runway 27R for New York at 18.25. The aircraft leveled off at FL310 31 minutes later. At 19.03 Shanwick Oceanic Control transmitted an oceanic clearance. At that time an explosion occurred in the aircraft's forward cargo hold at position 4L. The explosive forces produced a large hole in the fuselage structure and disrupted the main cabin floor. Major cracks continued to propagate from the large hole while containers and items of cargo ejected through the hole, striking the empennage, left- and right tail plane. The forward fuselage and flight deck area separated when the aircraft was in a nose down and left roll attitude, peeling away to the right at Station 800. The nose section then knocked the No.3 engine off its pylon. The remaining aircraft disintegrated while it was descending nearly vertically from 19000ft to 9000ft. A section of cabin floor and baggage hold (from approx. Station 1241-1920) fell onto housing at Rosebank Terrace, Lockerbie. The main wing structure struck the ground with a high yaw angle at Sherwood Crescent, Lockerbie causing a massive fire. The Semtex bomb which caused the explosion had probably been hidden in a radio cassette player and was transferred to PA103 from a Pan Am Boeing 727 flight, arriving from Frankfurt. The Popular Front for the Liberation of Palestine General Command (PFLP-GC) was probably the organization responsible for the bombing.
PROBABLE CAUSE: "The in-flight disintegration of the aircraft was caused by the detonation of an improvised explosive device located in a baggage container positioned on the left side of the forward cargo hold at aircraft station 700."

All four engines had struck the ground in Lockerbie with considerable velocity and therefore sustained major damage, in particular to most of the fan blades. The No 3 engine had fallen 1,100 meters north of the other three engines, striking the ground on its rear face, penetrating a road surface and coming to rest without any further change of orientation i.e. with the front face remaining uppermost. The intake area contained a number of loose items originating from within the cabin or baggage hold.

Engines numbers 1,2 and 4 had separated from the wing due to side loads (probably from a spiraling of the aircraft wing). These engines separated nearly at the same time since they were found in reasonably close proximity to each other in farmyards. They had struck the ground nearly in the horizontal position and with the ground in a softened state including one engine having penetrated into a farmers’ dung pit. Resulted in symmetrical hydraulic loads on the engine surfaces similar to a water impact, which opened up the surrounding cowls like a gull wing and squashed the larger engine cases against their blades in an oval pattern. See figure PA27-1

Engine position 3 was unique in that it fell a considerable distance from the other engines, having separated earlier in the breakup sequence. It was described by eyewitnesses as falling down from the sky while burning with a bright white glow. It struck the ground tailpipe first and both compressed itself by foreshortening in length by several feet as well as penetrating directly into the ground by several feet. While still mostly buried in the ground it still continued to burn. When the engine was dug out of its hole it was noted that it had penetrated a sewer pipe in below ground level (yet a second engine to end up in dung). See figures PA27-3, 4 & 6

The engines were recovered and taken to a building shed near an overhaul facility where mechanics and tools were available for some disassembly while under the watchful eye of the police.

Examination of the left-hand inboard engine position 2 revealed numerous unique scars and damage to both the inside and outside of the inlet cowl or engine intake. The damage to the inside of the cowl was both indicative of the entrance of foreign material as well as indicative of shedding of material from the fan blades them selves. In the final analysis it was concluded that the engine had sustained a massive ingestion event while operating at power sufficient to disable the engine (cause it to run-down below idle). See figures PA26-2, 3 & 7

Examination of the exterior surfaces of the inlet cowl for position 2 revealed that the skin surface facing the fuselage baggage area of the aircraft had been pock marked with scratches dents and holes as if a very high power shotgun had been fired directly into it. From the degree and metallic evidence visible in this damage it is possible to estimate the size/shape and velocity of the fragments that struck this inlet while in flight. In the final analysis is was concluded that the fragments were similar to those ingested by the same engine and were mostly aluminum skin fragments containing paint along with portions of aircraft interior to the skin. See figures PA26-4, 5 & 6

Examination of engine position 3, which is the inboard engine on the revealed that multiple remarkable events had occurred to this engine in sequence.

One notable event was the umbrella shaped mode of damage to the fan blades. These blades evidenced bending in the direction of rotation while at the same time having their tips forced back out of their normal plane of running position. This could only have occurred if a massive axial force was applied to this engine while it was no longer running at speed. Since the engine had obviously struck the ground tailpipe first, ground impact was ruled out in favor of an inflight event. See figure PA26-7.

Additional examination of this engine position revealed the remarkable evidence that a local circumferential portion of the nacelle inlet was severely axially crushed by several feet while in the same position severe fire damage was noted to the non-metallic portions (Nomex interior honeycomb). In addition the engine case structure corresponding to this area evidenced severe heat distress to the non-metallic rub strip material that is normally located surrounding the fan blade tips. Analysis of this evidence led to the conclusion that the inlet and fan case structure had been telescopically forced backwards over the gearbox section of the engine resulting in a magnesium gearbox fire which resulted in the local burning of the damaged structures which had been pushed over it. All of this had to have happened in the air since all the ground impact damage had occurred to the tailpipe piercing into the ground. See figures PA26-8 & 9

Also remarkable to this accident investigation was the condition of all four engine fan blade tip rub strips. In all four engines they exhibited extremely deep scoring that was both localized circumferentially (in the same clock position) as well tracking skewed out of plane in the fore and aft direction.

In conjunction with this damage was the observation that all engine fan blade sets also exhibited extremely severe localized rubbing on a small arc of blades sufficient to remove over a half inch of material length. Analysis of this damage concluded that it could only have occurred as gyroscopic loading as a result of a rapid change of axis of the engine centerlines while all four engines were spinning at high speed/power. See figure PA27-10

The evidence of gyroscopic loading to an engine involved in an accident had heretofore never been seen. It was then concluded that the engine pylon mounts could never withstand change of angle motion in the horizontal plane (yaw axis) sufficient to produce the necessary bending of the engine fan shaft to produce the observed rubbing. The horizontal strength of the pylon or engine mounts themselves would have failed (fused) first). Instead the change of axis had to be in the vertical or pitch axis direction.

As stated earlier all four engines exhibited the same degree of rub and at the same clock or circumferential position to the fan cases. Using the right-hand rule it was then possible to conclude that the axis change was indeed in the vertical direction with a pitch down and that a severe roll to the left was likely taking place at the same time.

Assessment of the likely impact on the engine as a result of this rub was made. It was concluded that the loss of fan flow capacity as a result of severely increasing the tip clearances to the case would result in a rundown of the fan rotors within five seconds such that any other later events would be only to a wind milling engine rotor. Since other events were clearly evident to the engines on this aircraft it is possible to relatively time them as well.

The position 2 left-hand inboard engine had been concluded to have a massive ingestion and fan blade damage event while it was running at power. This in itself would also have resulted in this engine running down within five seconds of this event. Since both this event as well as the gyroscopic event had occurred to this engine they must have occurred within the same five seconds.

The position 3 right-hand inboard engine had also sustained a massive frontal impact with an extremely large object while in the air. However this impact did occur after the gyroscopic loading event, since the former was at low power was the later was at high power.

It was then postulated that the following sequences took place.

1. An explosive rupture took place to the fuselage as shown in the location corresponding with figure PA27-5 and PA28-4

2. This initially resulted in ingestion and severe fan damage to position 2 engine. However before this engine could rundown, a massive pitch/roll event occurred to the aircraft in the downward direction resulting in severe and unusual gyroscopic loading to all the engines on the aircraft. The engine pylon mounts initially sustained this aircraft pitch loading although it is likely that the aft fuselage section supporting the tail plane could not sustain this load. See figure PA28-1

The nose section of the plane then peeled away to the right and impacted the no longer running engine position 3 tearing it from the wing in an axial separation while the aircraft was in a nose down attitude. This engine subsequently fell to the ground burning from a magnesium gearbox fire.

4. The remaining engines were then slung off the wings having separated from side loads as the wing spiral

An updated comment is offered relative to similar engine damage experience having been seen or not seen in other large transport engine aircraft. TWA800 was checked for evidence of similar damage and none was found. There was no large gyroscopic forces generated by its fuselage breakup and there were no explosive ruptures inline with the engine inlets.

However it was reported that the UT DC10 event in Chad did have evidence of ingestion into both wing engines.

Regarding the gyroscopic loading, both 747 events that lost the position 3 engines in flight CI and LY did have severe gyroscopic damage to these engines, which was caused when the engines pitched or yawed immediately after separating from the wing while running at high