Spanish investigators believe that a Bombardier Dash 8-300 crew's lack of understanding of the alternate landing-gear extension system forced the pilots to conduct a landing at Barcelona with the nose-gear retracted.
The Air Nostrum service to San Sebastian was being operated by regional carrier Denim Air but the undercarriage of the turboprop (PH-DXB) failed to retract after take-off.
Spanish investigation authority CIAIAC says the landing-gear alternate release door - which is located overhead in the cockpit - had probably been left partially open, but this was not detected during the pre-flight checks.
If this door is left open a bypass valve prevents pressurisation of the landing-gear and it does not retract when the pilot sets the gear lever in the "up" position.
There were storms in the vicinity and the pilots, concentrating on flying the aircraft in difficult weather conditions, "did not detect anything abnormal", says the inquiry.
But when they realised there was a problem with the landing-gear, it adds, their response indicated "insufficient knowledge" of the alternate extension system and the effect of the overhead door - even after it was closed.
CIAIAC says that cockpit conversations and the crew's subsequent performance of the emergency procedures also showed that neither pilot had in-depth knowledge of, or familiarity with, the quick-reference handbook.
The crew opted to return to Barcelona and the inquiry notes the captain's "resignation" to land without the nose-gear.
It touched down some 20min after take-off and came to a halt 43s later, with the nose in contact with the ground for the final 12s.
CIAIAC says evacuation of the 32 passengers was hindered by reluctance to leave the aircraft in the rain, while "many" passengers did not obey "repeated instruction" to leave hand-baggage behind.
Technical examination of the aircraft, after the 22 October 2009 event, found no malfunction that could have prevented normal operation of the landing-gear. CIAIAC says "human actions and omissions" resulted in the landing-gear alternate release door being left open improperly, and its condition remaining undetected by the crew.