Incident
On 8 September 2024, a Textron B200 aircraft, registration TF-NLA, operating a contracted passenger flight from Station Nord (BGNO) to Mestersvig (BGMV) under callsign FNA502, experienced a loss of cabin pressure. The incident occurred while climbing through FL250, about 44 nautical miles south of BGNO. A loud bang was heard from the aft cabin, followed by a rush of wind. The cabin altitude gauges rose rapidly, prompting an emergency descent.
Aircraft Information
The aircraft was a Textron B200 with two PT6A-42 turboprop engines, manufactured in 1997 (serial number BB-1597). It had a valid Certificate of Airworthiness. The cabin door upper forward locking pin (part number 101-430029-1) had accumulated 8,585 cycles since new, close to 86% of its 10,000-cycle airworthiness life limit.
Crew Actions
The Commander, as Pilot Flying, initiated an emergency descent, reducing power to idle, setting fine pitch, selecting flaps approach, and lowering the landing gear. The First Officer declared an emergency via SATCOM and squawked 7700. Neither crew member donned oxygen masks initially, as the Commander prioritized communication. When the cabin altitude briefly exceeded 12,500 feet, the cabin oxygen masks deployed automatically, but the crew did not use them. The aircraft descended to FL100, then returned to BGNO, landing safely at 15:57 UTC.
Investigation Findings
Investigation by SIA-Iceland revealed that the forward upper cabin entry door hook fractured due to intergranular corrosion. The crack initiated at multiple points on the threaded portion and propagated inward. The outer area of the fracture surface was corroded, indicating an aged crack, while the inner area was not corroded, suggesting a final failure event. The hook was made of 4340 high-strength low-alloy steel, and its strength was marginally above drawing requirements. The part had not reached its life limit and was not affected by Beechcraft Service Letter MTL-52-02.
Safety Recommendation
SIA-Iceland issued Safety Recommendation 24-045F014 T01 to Textron Aviation, recommending reconsideration (lowering) of the 10,000-flight-cycle life limit for door hooks, or design changes to improve endurance.