The Nimrod Review - Official Documents

The Nimrod Review
28
3.7.10 The fire would have considerably weakened the aircraft’s spar and the aircraft’s hydraulic systems would
have begun to fail as hydraulic liquid boiled and pipe unions melted. The loss of primary and backup
hydraulic systems and possible fire damage to flying control cables and pulleys, probably led to a
loss of control at some stage during the last 60 seconds of flight. During this period, the No. 7 tank
was probably subjected to a boiling liquid expanding vapour explosion (BLEVE), either as a result of
wing deformation or as internal pressure began to rise to a point at which it ruptured. The BLEVE was
probably the fireball reported by the GR7 pilot and Canadian witnesses.
3.7.11 Very shortly afterwards, and at a height of about 700 feet above ground level, the weakened starboard
wing failed, breaking from the aircraft and striking the tail structure. As the remaining aircraft structure
began to roll to the right, the port wing also failed and, shortly thereafter, the tail structure broke from
the aircraft. All four principal elements of the aircraft structure struck the ground within close proximity.
The accident was not survivable.
BOI’s Conclusions as to the Probable Physical Causes of the Accident
3.8
3.9
3.10
In summary, therefore, whilst the BOI was unable to determine positively the exact source or causes of the fire
which led to the loss of XV230 and its crew, 13 the BOI found that the following were the most probable physical
causes of the fire and explosion: 14
3.8.1 The escape of fuel during AAR, occasioned by an overflow from No. 1 tank, or a leak from the fuel
system (fuel coupling or pipe), led to an accumulation of fuel within the No. 7 Tank Dry Bay. Although of
a lower probability, the fuel leak could have been caused by a hot air leak damaging fuel system seals;
and
3.8.2 The ignition of that fuel following contact with an exposed element of the aircraft’s Cross Feed/SCP
duct.
The BOI also identified the following as being possible contributory factors to the accident:
3.9.1 The age of the Nimrod MR2’s non-structural system components;
3.9.2 The Nimrod MR2 maintenance policy in relation to the fuel and hot air systems;
3.9.3 The lack of a fire detection and suppression system within the No. 7 Tank Dry Bay;
3.9.4 The fact that the Nimrod Safety Case (NSC) did not correctly categorise the potential threat to the
aircraft caused by the co-location of fuel and hot air system components within the No. 7 Tank Dry Bay
(see further below); and
3.9.5 The formal incorporation of the AAR capability within the Nimrod did not identify the full implications
of successive changes to the fuel system and associated procedures.
The BOI further made a number of additional observations, including:
3.10.1 Changes to RAF Kinloss’ management structure as a result of Project Trenchard removed the SO1
engineer (OC Engineering Wing) from the station structure, with the consequence that engineering
personnel were distributed between the station’s two remaining wings under non-specialist leadership
and Queen’s Regulation 640 responsibility was delegated to a squadron leader. Both operational and
engineering witnesses believed that this change had had a negative effect on aircraft availability.
I consider this issue further in Chapter 13.
13 Given that the BOI was unable to investigate the wreckage at the crash site and it proved impossible to recover more than a few small components
from the aircraft.
14 BOI Report, paragraph 60 [2-44 to 2-45].
15 BOI Report, paragraph 61 [2-45].
16 BOI Report, paragraph 64 [2-45 to 2-46].
16
15