Bolt failure blamed for DC-10 cowling loss

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Boeing is to propose revised maintenance procedures for the engine nacelles on McDonnell Douglas DC-10s after a Continental Airlines aircraft lost a large part of the core cowling from its left-hand General Electric CF6-50C2 shortly after taking-off from Manchester in the UK.

Witnesses to the incident, which occurred in August last year while the DC-10-30 (registration N35084) was performing a standard instrument departure from Manchester, reported seeing "sizeable pieces of metal falling from the sky and landing on or near the verges" of a major road, according to the UK Air Accidents Investigation Branch (AAIB).

The largest piece of debris comprised a 1.2m x 0.6m stiffened sheet metal panel, says the AAIB, adding that "about 70%" of the right-hand side of the core cowl had departed the aircraft in all.

The crew of the DC-10 continued their flight to Newark, New Jersey unaware of the damage, noting only the loss of exhaust gas temperature (EGT) indication shortly after take-off.

Subsequent investigation determined that the sections of cowling had departed following fatigue failure of hinge attachment bolts. The AAIB was unable to establish the precise cause of the bolt failures, but noted that repairs had been carried out to the bolt-hole that contained the first bolt to have developed fatigue.

"Inspection of the parts held at the AAIB showed that only one of the three hinge fittings had remained on the cowl - the remainder having [been] torn out of the cowl structure, as had the lower locking clasps," it says.

Boeing - which has design authority for the DC-10 following its take-over of McDonnell Douglas - is proposing to amend repair manuals such that "if any damage, such as bolt hole damage, elongation or loose bolts, is noted in the area, then bolt replacement will be required", according to the AAIB. The manufacturer will also urge that inspections of the affected parts of the core cowling be carried out at 'C' check intervals - usually every 12-24 months.

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Source: AAIB