Interesting report in view of this accident Thanks ichris
Accident Report:
AS350B2, G-OROZ; 21 January 2001 at approximately 1521hrs
Front Seats
Both front seats had detached from the floor in the impact. Rescuers found the pilot still in his seat, lying across the rear seat occupants. It was evident that both front occupants had been thrown forward and to the right when their seats became detached. There was evidence that the pilot had been thrown against the cyclic stick and the instrument panel and his head had struck the door frame.
The front seats were the standard, original fit AS350 high-backed seat which is entirely of a mounded fiberglass construction. The seats were identified with part number 77125805 on the seat back. The shoulder harness inertia reel unit is attached at the bottom of the seat back. Longitudinal steel strips located on either side of the base of the seat pan allow the seat to be bolted to the 'C' section seat rails. The seat rails are locked in place in the cabin floor by turnbuckles which locate in slots in the bottom flange of the seat rails.
Both front seats had failed in a different manner on each side of the seat. The seat rails had torn out of the base of the pilot's seat, leaving the seat rails still attached to the cabin floor. The right side of the seat base had failed extensively due to vertical compression loading. The left side of the seat base was largely undamaged, except where the fiberglass had sheared around the periphery of the seat rail attachment due to tension loading.
The right side of the front passenger's seat base had failed the same manner as the right side of the pilot's seat base. On the left side, the entire seat rail had pulled out of the cabin floor due to the slots in the seat rail having been distorted sufficiently to allow the seat rail to become released from the turnbuckles. The outer section of the rear slot had failed in overloading and was missing. The seat rails were fitted with 'L' shaped brackets which overlapped the outer edges of the slots and were designed to limit the extent to which the slots could open up, but this proved ineffective due to the slots having experienced significant vertical as well as lateral distortion.
The failure of the front seat bases was inconsistent with the relative lack of damage to the cabin and in particular the cabin floor. Similar failures of the seat rail attachments at the seat base and the cabin floor attachment were seen in a previous fatal accident to an AS350 helicopter with the same type of seats (AAIB Accident Report 4/96 refers). The seats have also been known to fail even under fairly gentle impact loads, as reported in AAIB Bulletin 1/2001 in which an AS355 helicopter made a forced landing on the roof of a house and in which the occupants sustained no injuries.
Although the AS350 fiberglass front seats met the crash worthiness testing requirements applicable at the time that the helicopter was certificated in 1978, subsequent experience proved these requirements to be inadequate. Accordingly in 1989 the FAR Amendment 25 regulations revised the certification loading requirements upwards considerably. The same requirements are reflected in JAR 27.561:
Seats designed to the latest specifications which are installed on the current generation of new helicopters by necessity have a substantial metal frame to enable them to meet the new design criteria. These seats are available as a customer-specified option on the AS350B3 which is the latest variant of the AS350.
Eurocopter Letter Service No. 1424-25-99 was issued in November 1999 to advise operators that the new crash worthy seats could be retrofitted to earlier variants of the AS350 under an optional Service Bulletin (SB No. 25.00.57) issued in May 1999. In view of the cost and time involved (6 man-weeks) to perform this modification, it is unlikely that many operators would have opted for the improvement, particularly if they had been unaware of the deficiencies of the fiberglass seats.
LetterService No. 1424-25-99 also recommended that operators who opted not to install the new crash worthy seats should modify their fiberglass seats in accordance with Eurocopter SB No. 25.00.63. issued in 1999. This SB was issued in response to the Safety Recommendations made in previously mentioned AAIB Formal Report 4/96. The SB adds 4 additional plies of fibreglass to the lower seat pan and introduces new 'T' section seat rails. The SB is recommended by Eurocopter but has not been made mandatory by the DGAC or CAA.
EASA Safety Information Bulletin - Eurocopter AS350 and AS355 helicopters - Improvement of Pilot’s and Co-pilot’s Seats