Sir - I refer to the article "Maintenance mistake threatened Transavia Boeing 737 flight" (Flight International, 16-22 April, P7) and, in particular, to the reference made to TAP-Air Portugal. I would like to comment as follows.
Aircraft registration PH-TSW, operated by Transavia, underwent a heavy maintenance check by TAP-Air Portugal, in November 1996. The right-hand stabiliser, trimtab and elevator were removed and re-installed.
On 9 February this year, we were informed by Transavia that the aircraft's crew had made a precautionary landing on 8 February following abnormal vibration during a commercial flight. A TAP engineer was sent to Nuremburg and co-operated with Transavia, the German civil-aviation authorities and a Boeing inspection team on the first inspection performed to the aircraft after the incident.
From the date of the incident until now we have been in close contact with Transavia, the Portuguese civil-aviation authorities, the German civil-aviation authorities and Boeing. As far as we know, none has yet produced a final report.
TAP conducted an internal investigation (the result of which was made available to the involved parties) which did not show evidence of maintenance malpractice or disregard of maintenance procedures as defined by the manufacturer.
On 13 February, Boeing told us that a service-related problem (SRP) had been initiated. Operators were asked to check elevator-tab push-rod bolts and nuts. An update on the progress of the SRP will be provided by 29 April. TAP has been informed, however that, so far, three loose nuts have been found and that at least 108 nuts showed inadequate run-on torque.
In view of the apparent lack of failsafe design of the elevator-tab push-rod mechanism, TAP suggested to Boeing on 21 February that it should consider an improvement on the design of the control-rods attachment with a bolt-retention device. Boeing said later that, after the root cause has been identified, the SRP team will develop corrective action.
Although no final report has yet been produced, I would like to emphasise that it appears evident that the cracks detected in the stabiliser assembly of the Transavia aircraft were a consequence of a possible failure of the elevator-tab push-rod mechanism, and not of any intrinsic structural failure likely to be detected in previous inspections, as may be inferred from the article.
There was a previous incident involving a 737-500, reported by Boeing in May 1996, where one of the bolts which secure the elevator-tab control rods to the crank assembly on the right elevator was loose, and one was missing, along with its nut. According to a message which Boeing sent TAP on 28 February, the reported incident may be similar to the one involving the Transavia aircraft.
Jorge Sobral
M&E General Director
TAP-Air Portugal
Lisbon, Portugal
Source: Flight International
