Human error, faulty design behind Saras crash: probe

BANGALORE - Wrong selection of mode switch or failure to re-start the engine during the flight trial of the faultily designed light transport aircraft Saras led to its crash March 6, 2009, the investigation by the Indian aviation regulatory authority said Thursday.

“Either wrong selection of mode switch or non-pressing of start switch is the most probable cause for turboprop engine not relighting (restarting) during the test flight of the Saras P2 aircraft, resulting in its fatal crash,” the final report of the Director General of Civil Aviation (DGCA) concluded on the accident.

The two pilots of the Saras and an engineer of the Indian Air Force (IAF) were killed when the aircraft plunged to the ground near Bidadi, about 30 km from here.

The twin-engine second prototype, designed and manufactured by the state-run National Aerospace Laboratories (NAL) of the Council for Scientific and Industrial Research (CSIR), was test flown by chief test pilot, Wing Cdr.K. Praveen, test pilot Dipesh K. Shah and flight test engineer, Sq. Ldr.S.Illyaraja of the IAF’s Aircraft System & Testing Establishment (ASTE).

The board of inquiry, instituted by the DGCA to investigate the crash, also pointed out that NAL failed to design suitable control surfaces to attain the prescribed limit and prior to formulating the Pratt & Whitney engine relight procedures in air.

“Design improvement on control surfaces is required even for flight testing purpose to enable the crew fly the aircraft manually without getting into fatigue level,” DGCA’s inspector of accidents C.P.M.P. Raju said in the 75-page probe report.

The regulator also recommended NAL to consult other aircraft manufacturing industries to explore the convenient limit of control forces for easy manoeuvrability by pilots.

Flying the experimental Saras for the first time, the pilots attempted to switch off and relight in midair (about 9,000 feet) one of the two engines (PT6A-67) as part of the mandatory flight development programme requirement.

“After ascending to its designated height of 9,000 feet, the left engine was switched off. When the crew attempted to relight or restart it after a minute, it failed, resulting in the aircraft losing height, going out of control and crashing,” the report said.

All the three on board were charred to death and were on their seats. There was evidence of fire after the crash, while the aircraft fuselage was broken from rear of the main plane and found in an inverted position. The aircraft was completely destroyed due impact and fire.

“At about five minutes prior to crash, when some abnormal behaviour of the aircraft was felt by the pilots, the co-pilot was hilariously telling commander ‘road is there for emergency’ and also advised FTE (flight test engineer) for placing readiness of parachute for emergency.

These parachutes were not used by the pilots/FTE in the accident. It is not known whether the pilots were trained to operate the parachutes in case of exigencies. Records provided to the investigation are insufficient to show their training on parachutes exercise,” the report said.

Incidentally, NAL flew the same aircraft at the Aero India 2009 air show in Bangalore without the DGCA’s permission.

The multi-role Saras was developed for use by the military and civil aviation sector at an estimated cost of Rs.150 billion though the project was conceived in the mid-1990s.

Named after the Indian crane, the airframe of Saras-PT2 was built with lighter composites to reduce its overall weight by about 400 kg from its first prototype, which was overweight by about 900 kg.