History of the Flight
On 6 October 2013, a SAAB 340B aircraft, registration HS-GBG, operated by Siam General Aviation Company Limited as Nok mini Airlines flight 5E950, departed Chiang Mai International Airport at 07:25 hours for Udon Thani Airport. The flight carried 28 persons: two pilots, one cabin crew, and 25 passengers.
After engine start at 07:23:44, a single chime warning sounded. The pilot expressed doubt about the malfunction but continued. At 07:30:18, during landing gear retraction after takeoff, a second chime occurred. The pilots discussed that the warning likely indicated hydraulic system loss, but the pilot decided to continue as the landing gear was already down. A third chime sounded at 07:35:31.
At 08:43:41, a fourth chime prompted the pilots to address the insufficient hydraulic pressure by selecting the hydraulic pump control switch to OVRD position. The pilot noted there was no time to consult the Aircraft Operations Manual (AOM) and that hydraulic pressure was at zero. At 08:45:35, the pilot reported landing gear problems and held at 2,500 feet. The co-pilot attempted to retract landing gear and flaps but could not. The autopilot disengaged twice.
At 08:48:01, both pilots followed the Abnormal Checklist for Hydraulic Light ON, Emergency Pressure Normal and Main Pressure Low by using the hand pump (auxiliary system). They successfully extended the landing gear and retracted the flaps. At 08:52:12, three consecutive chimes sounded. The pilots discussed flap and gear extension issues, eventually extending the flaps.
At 09:02:52, the pilots performed landing procedures. The pilot instructed the co-pilot to use full reverse thrust due to possibly inoperative brakes. At 09:05:05, while vacating runway 30 onto taxiway C, the pilot was controlling the aircraft. The co-pilot twice suggested using the hand pump, then proposed stopping and requesting a tow.
The aircraft veered left off taxiway C, passed the intersection of taxiways C and N, struck the concrete base of an aerodrome information sign, and came to rest. The aircraft was destroyed. All occupants were safe.
Aircraft Information
The SAAB 340B was equipped with a hydraulic system that included pumps, accumulators, and a hand pump for auxiliary operation. The Warning Annunciator System (WAS) provided chimes and lights for system anomalies. The aircraft had a deferred defect related to the hydraulic system, but details are not specified in the report.
Personnel Information
The pilot and co-pilot held appropriate licenses. The pilot assigned the co-pilot as pilot flying for takeoff. Both discussed the recurring warnings but did not fully consult the AOM during the flight.
Causes
The investigation determined that the hydraulic system malfunctioned during the flight, and the pilots did not completely and correctly follow the Abnormal Procedures in the Aircraft Operations Manual.
Contributing Factors
Contributing factors included the pilots' failure to properly execute abnormal checklists and their decision to continue without fully resolving the hydraulic issue before landing.
Safety Recommendations
The report includes safety recommendations aimed at improving pilot adherence to procedures and enhancing crew resource management.