6th of October 2013, Blog #559
A Saab 340B was scheduled to operate a domestic flight from Chiang Main International Airport to Udon Thani Airport, in Thailand. The engines were started for the ~270 miles (~430 km) flight at 07.23 lt (local time), with the co-pilot as pilot flying (PF) and the captain as pilot monitoring (PF). During the engine start, a single chime was heard as an aural warning that a malfunction had occurred, it was unclear to the crew what the malfunction was.
The aircraft nose section with the failed nose landing gear (Source; AAIC report)
At 07.30 lt the aircraft lifted off from runway 36 and climbed out towards its destination. With a positive rate of climb indicated, the gear was selected up and a single chime was heard again, this time identifying the loss of the aircraft's hydraulic system, causing the landing gear not to retract, However, the Captain decided to continue the flight because the gear was down. 5 minutes later the single chime was heard again, the accompanying warning light had not been seen before by the captain. The flight continued without further incident and at 8,43 lt the PM contacted ATC to request an ILS approach to runway 30 at Udon Thani. A few seconds later the single chime sounded again, initiating a discussion between the pilots on how to operate the flaps and landing gear systems as the hydraulic system pressure was too low. (pressure was actually zero).
At 08.45, while 5 miles from the runway, the PM contacted ATC to inform them about the landing gear issue, requesting (and receiving clearance for) a holding at 2500 feet. While climbing to 2500 feet the captain assumed PF duties, while the copilot assumed PM duties. The PM then unsuccessfully attempted to operate the flaps and landing gear. 3 minutes later, at 08.48 the crew performed the Abnormal Checklist, Hydraulic Light ON, Emergency Pressure Normal and Main Pressure Low in the AOM, by using the hand-pump (auxiliary system). They were able to extend the landing gear and retract the flaps.
ATC queried if the flight required assistance which was rejected by the crew. The co-pilot asked the pilot whether the green light should illuminate when the landing gear was extended. After that, they were able to extend the flaps.
The aircraft after recovery, during part-0ut (© Steve Ozel) At 08.55 the captain contacted ATC requesting an ILS approach, and informing them that flaps and gear were extended. A normal approach was flown, followed by an uneventful landing using full reverse thrust as the brakes were suspected to be inoperative. While vacating the runway the co-pilot suggested using the handpump of the auxiliary hydraulic system, to stop the aircraft and getting a towtruck to tow the aircraft to the ramp. ATC was contacted about the necessity to stop the aircraft on the taxiway. At that time the crew was unable to stop the aircraft while the nose wheel steering system had failed as well. At 09.07 lt a triple chime a triple chime came on, and the co-pilot reported that they hit something. The pilot gave the order to shut down the engines. The co-pilot read back the order to shut down the engines and set the parking brake. There were no injuries to passengers and crew.
The aircraft shortly after the accident (©Richard Barrow) After the accident, the Aircraft Accident Investigation Committee of Thailand (AAIC) launched an investigation with the aid of several accredited representatives.
In their investigation report, the AAIC concluded that the probable cause of the accident was;
Failure of the crew to follow the Abnormal Procedures in the Aircraft Operations Manual to solve the hydraulic system malfunction when the single chime came on several times, during the flight.
Failure of the crew to perform to correctly perform and complete the Abnormal Procedures on Hydraulic Fluid Lost
After landing the crew taxied the aircraft with inoperative brakes and nose wheel steering due to loss of pressure in two accumulators
The crew lost control of the aircraft veered off the taxiway and hit the concrete base of the aerodrome information sign.
Saab 340B Hydraulic System (Source; AAIC report)
Damage to the aircraft was so extensive, it was written off, damaged beyond repair. The AAIC report, on which this blog is based, is available for more detailed information on this accident by clicking on the .pdf file below;