History of the Flight
On 15 August 2014, Jetstream 3102 G-GAVA departed Belfast City Airport at 1745 hrs on a scheduled commercial flight to Doncaster Sheffield Airport with one passenger and two pilots. The commander, serving as pilot flying, conducted an uneventful departure, cruise, and approach. The 1820 hrs ATIS reported wind from 260° at 5 kt, visibility greater than 10 km, few clouds at 3,000 ft aal, temperature 17°C, and QNH 1019 hPa. Although Runway 02 was active, the crew requested and received approval for a visual final approach to Runway 20. The calculated landing mass was 5,059 kg, requiring a target threshold IAS of 101 kt.
The aircraft touched down at 1836 hrs at 102 kt IAS with a peak normal acceleration of 1.3 g. The commander moved power levers aft to ground idle then reverse. As the aircraft decelerated, he returned the levers to ground idle and asked the co-pilot to set RPM levers to taxi. At 65 kt IAS, eight seconds after touchdown, the left wing dropped suddenly, the aircraft yawed left, and directional control was lost despite rudder and nosewheel steering inputs. The aircraft ran off the left side of the runway, turned approximately 90°, and came to rest on grass resting on its baggage pannier, right landing gear, and left wing. The left landing gear had collapsed.
The commander pulled both feather levers and switched the Electrics Master to emergency off. The co-pilot transmitted to ATC, who confirmed emergency services were en route. The co-pilot assessed the passenger as uninjured and chose the rear left cabin door for egress; the door released but could not open fully as the sill was at ground level, yet all occupants evacuated without injury. The aerodrome controller activated the crash alarm at 1836 hrs, and Rescue and Fire Fighting Service vehicles arrived at 1838 hrs, by which time occupants were clear.
Recorded Information
The aircraft was equipped with a 30-minute Cockpit Voice Recorder and a Flight Data Recorder (FDR) that captured the landing. The FDR recorded 116 hours of operation with five parameters: pressure altitude, heading, airspeed, normal acceleration, and a VHF discrete. A Terrain Awareness and Warning System recorded 30 parameters at higher sampling rates. Review of 82 previous landings found no concerns; the highest normal acceleration at touchdown was 1.72 g. The accident touchdown occurred at 1835:52 hrs with IAS 102 kt, normal acceleration 1.3 g, and rate of descent approximately 245 ft/min (4 ft/sec), within the design limit of 10 ft/sec at maximum landing weight. A normal acceleration spike was recorded at 65 kt groundspeed, indicating landing gear failure.
Runway Marks and Aircraft Damage
Runway marks began approximately 370 m from threshold markings, first from the top of the left landing gear cylinder after it folded, then from the left propeller striking the surface. The left landing gear broke away from its mounts due to forward pintle housing failure; two sections stayed attached to the pintle spigot but the gear remained connected by the radius arm and hydraulic pipelines. The left propeller blades were badly damaged, the left aileron balance horn separated and lodged in soft ground, the left wingtip sustained abrasion causing a fuel leak, and the baggage pannier and anti-collision beacon suffered considerable abrasion.
Landing Gear
The Jetstream 31 main landing gear leg comprises a cylinder (DTD 5094 aluminium alloy) and an inner sliding tube with wheel and brake assembly. The cylinder attaches to the airframe via a yoke onto steel spigots bolted through pintle housings. Upper surfaces of forward and rear pintle housings have machined flats acting as weak links to allow gear detachment without fuel tank damage under excessive loads. In this accident, the forward pintle housing failed along the machined flat. DTD 5094 is known to be susceptible to stress corrosion cracking (SCC), with similar failures on other Jetstream 31 aircraft. SCC in the forward pintle housing occurs when the forward face rotates against the spigot bearing during gear extension/retraction, causing abrasion, degradation of surface protection, corrosion pits, and cracking. Later Jetstream 31 and Jetstream 32 cylinders use L161 alloy, not susceptible to SCC.
Previous Occurrence
On 8 March 2012, the same aircraft (then registered G-CCPW) experienced a right main landing gear failure at Isle of Man Airport. The investigation found intergranular corrosion/stress corrosion cracking of the forward pintle housing as the cause, leading to a Safety Recommendation.
Stress Corrosion Cracking
Stress corrosion cracking occurs when susceptible metals under tensile stress in a corrosive environment develop cracks. Initiation typically follows compromise of protective surface finish, allowing corrosion. Cracks propagate along grain boundaries until critical length causes sudden overload failure. SCC in Jetstream 31 main landing gear forward pintle housing was first identified in 1985. The 2012 G-CCPW report documents the history. At that time, UK CAA AD G-003-01-86 and BAE Systems SB 32-A-JA851226 Revision 4 required high-frequency eddy current (HFEC) and visual inspections. Heroux-Devtek SB 32-19 Revision 3 specified visual inspections every 300 cycles/3 months in situ and HFEC inspections every 1,200 cycles/1 year with gear removed. The G-CCPW investigation found these inspections had not been successful in detecting cracks.
The current investigation determined that a design solution implemented by the manufacturer after the 2012 accident—a protective washer on the forward pintle housing—did not meet its original intent. A fouling condition caused rotational movement of the washer on G-GAVA, degrading surface protection and creating conditions for corrosion pits, from which a stress corrosion crack initiated and propagated.