Despite being categorised as mandatory for the pilot’s seat by the aircraft manufacturer, a secondary seat stop modification designed to prevent uncommanded rearward pilot seat movement and potential loss of control was not fitted to VH-FRT, nor was it required to be under United States or Australian regulations.
Response to safety issue by the Civil Aviation Safety Authority
CASA has reviewed the purpose and function of the secondary seat stop modification and concluded that this modification in itself would not address an unsafe condition. CASA issued Airworthiness Bulletin (AWB) 53-010 in July 2016 to clarify the legislative requirements relative to the Cessna Supplemental Inspection Documents (SIDS) inspection program. The AWB addresses the incorporation of Cessna Single Engine Service Bulletin SEB07-5 where CASA’s position is that this modification, while highly recommended, does not have a legislative requirement for incorporation.
The US Federal Aviation Administration (FAA) released Special Airworthiness Information Bulletin (SAIB) CE-09-10 in February 2009, which alerted operators to the availability and potential safety concern that is addressed by this particular modification. SAIB’s are issued with the following caveat:
At this time, this airworthiness concern is not an unsafe condition that would warrant AD action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.
As such, the FAA did not, and has not since decided that regulatory action was appropriate for this condition.
The primary interest for CASA regarding the findings of this investigation is the lack of the seat rail stop. This stop was installed following the 100 hourly/annual inspection but was likely not present at the time of the event. As pilot maintenance allows for the removal of aircraft seats, it is reasonable to conclude that either a seat was removed and the seat rail stop was not reinstalled or the seat rail stop had simply dislodged. If the former is correct, then the factors that led to the seat rail stop not being re-installed would also have the potential to be present in a secondary seat stop (i.e. if the seat rail stops were not reinstalled, why would the secondary seat stop be installed). The question was raised regarding similar systems for other aircraft types that do not have a similar modification available.
CASA believes the appropriate course of action to address this condition is to require the inspection of the seat stop hardware (i.e. seat stop hardware/mechanism) as part of the pilot’s daily inspection in addition to the current requirements to check related hardware such as seat belts. CASA intends to legislate this through Schedule 5 of the Civil Aviation Regulations (CAR) and to also require the Australian Parachute Federation (APF) to amend their jump manual to reflect this requirement. That process will involve industry consultation. In the meantime, an AWB will be issued to draw attention to this requirement pending the legislative change to Schedule 5.
ATSB comment/action in response
Historical incident and accident data has shown that inadvertent rearward movement of the pilot seat in single engine Cessna aircraft is a safety issue that should be addressed.
Cessna designed, manufactured and mandated the secondary seat stop modification through Single Engine Service Bulletin SEB07-5 as a method of preventing seat slide occurrences. The modification was offered free of charge, inclusive of parts and labour, to all relevant single engine Cessna aircraft owners world-wide. These actions by the manufacturer are indicative of the significance of the safety issue.
While the intention of the Civil Aviation safety Authority (CASA) to draft an AWB for seat, seatbelt and stop inspections is welcomed, the ATSB remains concerned that due to Australian regulations for aircraft maintained in accordance with Maintenance Schedule 5 the modification is not mandatory in Australia.
As a result, the ATSB issues the following safety recommendation.