Hi Jess:
Have unmodified aircraft been flying, and if so, why have they been grounded at this particular time? Is there an engineering reason, or a political reason?
The HP air pipe replacement program is borne out of an incident on XV227 in Nov 04, when an SCP pipe burst and nearly caused the loss of that aircraft. Among many of the recommendations in the subsequent investigation report was a requirement for all HP air pipes on a selection of aircraft to be examined for condition and then a lifing and maintenance policy be considered depending on the outcome of the examinations. BAeS carried out the work and they found some areas of concern in both the crossfeed pipe and the engine bays. They suggested a pipe life which was less than the existing age of all the pipes in service (except the SCP pipework; already replaced). Given that BAeS are also the design authority, the RAF had no alternative but to immeditely declare all of the pipes on all of the aircraft as LIFEX at that time. But, we didn't have spare pipes and we didn't have the manpower, so it was declared that we will change them all before 31 Mar 09. Thats the politics.
Regarding the safety side of this subject, use of the SCP and the crossfeed pipe in the air is prohibited and those pipes are at low temperature and depressurized in flight. The pipes in the engine zones remain in daily use, without any restrictions, and become more vulnerable to failure as each day passes and they are doubtless a growing hazard. However, and this is a very important point, those pipes are monitored by hot air leak detectors, instrumentation, a fire warning and suppresant system and the crew have robust drills to deal with even the most explosive failure. The worst case failure will result in an engine being shut down by the crew (not an engine fire or failure). This robust mitigation reduces the risk of losing the aircraft, due to a pipe failure, to a neglible level. We are more at risk of crashing due to birds, fuel contamination or pilot error than an HP pipe failure. Consequently, the impending grounding is not a flight safety issue at all. All the aircrew know this.
Having stated that all the pipes on all the aircraft will be replaced before 31 Mar 09, the IPT is worried that if a pipe fails in flight after that date, regardless of any drill that will successfully and safely deal with it, that they, the IPT, will be seen to have been negligent with airworthiness. Therefore, those aircraft without the new pipes will not fly on or after 1 April. Unfortunately, we will not have enough aircraft with new pipes to meet all of the tasks. The task that will drop off is the overseas operational one.
So, its a polical issue within the IPT to ground some aircraft. IMHO its a flawed decision to ground them, for these self serving reasons within the IPT, when those aircraft are all needed. Soldiers on the ground will suffer due to the absence of the Nimrod. I despair that the IPT, having been briefed ad nauseum that the aircraft is not at risk of a catestrophic or critical failure, is allowed to do this to the troops in theatre. They risk a bullet in the head and we risk an engine-out on an overpowered aircraft. Someone needs to re-think his risk analysis.
Ed Sett