Serious incident ATR 42-500 F-GPYF,

ASN Wikibase Occurrence # 319708

This record has been locked for editing.

Date:	Sunday 25 March 2018
Time:	21:18
Type:	ATR 42-500
Owner/operator:	HOP!
Registration:	F-GPYF
MSN:	495
Year of manufacture:	1996
Total airframe hrs:	35123 hours
Cycles:	34805 flights
Engine model:	Pratt & Whitney Canada PW127E
Fatalities:	Fatalities: 0 / Occupants: 51
Aircraft damage:	Minor, repaired
Category:	Serious incident
Location:	Aurillac Airport (AUR) - France
Phase:	En route
Nature:	Passenger - Scheduled
Departure airport:	Paris-Orly Airport (ORY/LFPO)
Destination airport:	Aurillac Airport (AUR/LFLW)
Investigating agency:	BEA
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
An ATR 42-500, operated by Hop! as flight 235 sustained damage to the left-hand wing/body fairing while on a flight from Paris to Aurillac, France. At the start of the descent the left main gear door separated from the aircraft.
A safe landing was carried out.

Contributing factors
The loss of the nut on the rear assembly of the left main gear door resulted in the separation of the left main gear door from the aircraft. However, the exact cause of the loss of the nut could not be determined.
However, examination of the left and right landing gear door fasteners of F-GPYF, as well as those of the HOP! fleet of ATR 42 aircraft, revealed defects in the conformity of these assemblies.
The investigation revealed errors in the generic maintenance documentation that may lead to the installation of out-of-date screw/nut combinations. The consequences of these deviations from good practice on the performance of the assembly could not be precisely determined during the investigation but may lead to a loss of function of the assembly.
Thus, the following combinations of organizational and human factors potentially contributed to the loosening and subsequent unscrewing of the nut on the rear assembly of the left main landing gear door:
- The ATR maintenance documentation concerning the choice of nuts to be used as an alternative to P/N IPC is complex and contains errors that could lead to an inadequate P/N nut choice ;
- The information on the torque to be applied on this nut and for all these alternatives was missing from the ATR maintenance documentation;
- The generic ATR maintenance documentation allows the reuse of nuts without checking their self-locking capacity. The work card for the removal/installation of train doors does not specify that it is a self-locking nut and does not require checking its self-locking capacity or its replacement by a new nut.

Accident investigation: