Data recorder shows blades in fine-pitch that would have created sudden drag and could explain power loss

Information from the crashed Luxair Fokker 50's flight data recorder has revealed that, on approach to Luxembourg Findel Airport, the propellers entered the low-speed fine-pitch regime normally only usable on the ground. This would have provided a considerable amount of sudden drag, forcing the aircraft to descend to retain flying speed, and might explain why the engines had suddenly stopped producing power (Flight International, 19-25 November).

According to a European aviation authority, Fokker Services re-issued a notice to operators on 14 November advising them of an anomaly that had occurred previously that could lead to an event such as this. A stop controlled by a solenoid switch normally prevents the power levers being retarded into the ground fine pitch sector while the aircraft is airborne, but during the first 16s after the landing gear has locked down, it had been found that the solenoid could trip out. The notice to operators (No 137) was reissued to remind airlines of this. Although a modification to the anti-skid system which would also correct the anomaly had been developed by Fokker, Flight International has learned that it had not been embodied on the crashed Luxair aircraft. There is also a manual switch that enables the solenoid switch to be tripped to enable the pilots to engage ground fine pitch, but there is no indication at this stage as to whether it had been selected. Until the mishap, however, the instrument landing system approach had been stabilised with no indication of malfunction or crew concern.

The captain and a passenger survived the 6 November Luxair accident, but two crew and 18 passengers were killed when the aircraft suddenly veered to the right of the extended centreline before crashing in a field in fog.

Authorities have said that the Luxair accident and the crash on 11 November of a Laoag Airlines Fokker F27 in the Philippines are not technically connected, although the Philippine aircraft suffered power loss in one of its engines soon after take-off.

Source: Flight International