Scandinavia's SAS Group is claiming to have discovered door-valve problems in two-thirds of its grounded Bombardier Q400 turboprops, three months after a loose door-valve O-ring led to a landing accident in Copenhagen.
SAS grounded the type permanently after the accident on 27 October last year, the third gear-related crash in just a few weeks involving a Scandinavian Airlines Q400.
The company says its technical department has checked the Q400 fleet and found problems in 63% of the door sequence solenoid valves it inspected after the grounding.
Danish accident investigation commission HCL said last November that an O-ring had migrated from the valve and blocked an orifice in the landing-gear actuator assembly. This blockage prevented the starboard main landing-gear from deploying, forcing the Q400 to land at Copenhagen with the gear retracted.
SAS Group says it is waiting for HCL's findings, but insists: "SAS had no possibility of - and cannot be blamed for not - discovering these problemsin the course of its maintenance work."
HCL says a loose O-ring could not normally have migrated to the landing-gear because certain components in the aircraft, notably a mechanical sequence valve, prevented passage.
But SAS technicians replaced both the door sequence solenoid valve and the mechanical sequence valve on the aircraft in question just days before the accident.
HCL has suggested that, during the replacement, the rogue O-ring was unwittingly transferred - perhaps in one of the unions - to a position within the aircraft from which it could freely travel to the landing-gear assembly.
SAS Group claims that the door sequence solenoid valve has a "construction error" and that the component is being modified.
Bombardier, however, is refusing to be drawn into an argument. The manufacturer says: "From our point of view there's no new evidence that alters the conclusions of the Danish investigators last November."
It declines to respond to SAS' comments about the door valve because the company sees no value in focusing on this single component outside the context of a detailed inquiry report.
HCL is still investigating the two preceding accidents which contributed to SAS Group's decision to ground and withdraw the Q400 fleet. Both involved main landing-gear collapses which have been traced to actuator corrosion.
Source: Flight International
