On 6 April 2006, an incorrect response to a propeller malfunction, by the crew of an SAS Dash-8-Q400, resulted in an unstable single engine approach, and operation of the remaining engine outside limits. The aircraft landed safely at Kalmar, Sweden.
The following is an extract from the History of Flight in the SHK Report on the accident:
"At this point the power situation of the engines was extremely asymmetrical, with -6% Tq from the right engine and 125 % Tq from the left engine. Printouts of the information recorded by the Flight Data Recorder (FDR) show that the maximum aileron and rudder deflection was used to be able to control the aircraft in this configuration. At a later point in the approach the commander asked “Why have we…?” The first officer answered: “We haven’t feathered - that’s why”."
This is the Summary from the report published by the Swedish Accident Investigation Board:
"The aircraft departed from Stockholm/Arlanda Airport for a scheduled flight to Kalmar. On board were four crew members and 69 passengers. The first part of the flight proceeded normally, with the commander as PF (pilot flying). During the flight a technical failure occurred which meant that the right side propeller overspeeded. According to the emergency checklist a number of actions are to be taken, ending with feathering the faulty propeller and switching off the engine to reduce the air resistance (drag) of the propeller. The commander decided however to keep that engine at flight idle during the approach, which meant that the angle of the propeller blades remained flat to the aircraft direction, thereby causing severe drag. This severe drag caused great control problems for the aircraft and the commander thus had to use a power output from the other engine that exceeded the maximum permitted power. The approach was not stabilised and the final stage was at a very low height. The crew had not practised dealing with faults in this system during approach and landing, and considered that the emergency checklist was unclear. During the three week period immediately preceding the incident, three failures of the same type occurred on this individual aircraft. In no case had the crew completely followed the instructions in the emergency checklist. Nor had the technical fault been located correctly. The incident was caused by the fact that the emergency checklist was not completed, and a combination of the pilots not being aware of the risks due to leaving an unfeathered propeller in flight idle, unclear operations documentation concerning the propeller overspeeding type of propeller fault, and deficient follow-up of previous similar occurrences.
It is recommended that EASA:
- Makes efforts to set up a working group, with representatives of the manufacturer and the airline, and possibly other operators of the Q 400. The purpose should be to improve both the content and the method of application of the emergency checklist for the Q 400 (RL 2007:12e R1)."
For further information see the full report published by the Swedish Accident Investigation Board (SHK).