Flight Details
On May 25, 2011, M/s Air Charter Services Pvt Ltd. offered their aircraft VT-ACF for a medical evacuation flight to pick up a critically ill patient from Patna. The aircraft departed Delhi for Patna with two crew members, two doctors, and one male nurse. The flight to Patna was uneventful.
After boarding the patient and one attendant, the aircraft, with a total of two crew and five passengers (including the patient) per the passenger manifest, departed Patna at 20:31:58 IST. The flight plan filed with Patna ATC specified route W45-LLK-R594 at FL260, with an estimated time of departure of 22:00 IST and an estimated enroute time of 2 hours. The crew conducted a self-briefing of the weather, which was recorded on the flight plan. Weather at Patna at departure was 3000 meters visibility with haze. Total fuel on board at Delhi departure was 1516 liters.
Accident Sequence
The aircraft climbed and cruised at FL260. After handover from Varanasi Area Control, the aircraft contacted Delhi Area Control (East) Radar at 21:53:40 IST, squawking code 3313. At 22:02:05 IST, the crew requested a 10° left deviation due to weather, which was approved. At 22:05:04 IST, the crew informed of a critical patient on board and requested priority landing and ambulance upon arrival, which was approved.
The aircraft was handed over to Approach Control on 126.35 MHz at 22:28:03 IST. At 22:28:18 IST, VT-ACF contacted Terminal Approach Radar (TAR) while maintaining FL160. At 22:32:22 IST, the aircraft was instructed to continue heading to DPN VOR and cleared to descend to FL110. At 22:36:34 IST, the TAR controller informed the aircraft of weather on heading 330°, to which the crew replied affirmatively and requested a left heading. At 22:38:12 IST, the controller cleared the aircraft to a left heading of 285°, which was acknowledged. The aircraft began a left turn; while passing heading 289°, it climbed from FL125 to FL141.
At 22:40:32 IST, the TAR controller made three calls to VT-ACF. At 22:40:43 IST, the aircraft transmitted a weak call: “Into bad weather,” at which point it had climbed to FL146. The aircraft then began a tight right turn at low radar ground speed and descended rapidly from FL146 to FL016. At 22:41:32 IST, the TAR controller called again, and the aircraft transmitted another weak call: “Into bad weather.” The controller made repeated calls on 126.35 MHz and 121.5 MHz until the radar blip became stationary at a radial of 145 degrees and 15.2 nm from DPN VOR at 22:42:32 IST. All attempts to contact the aircraft failed.
Aftermath
The TAR controller informed the duty watch supervisor and the ATC tower. At 22:50:00 IST, the tower reported a call from the city fire brigade confirming that an aircraft had crashed near Faridabad in a congested residential area known as Parvatia Colony. Local residents and police attempted to extinguish the fire and extricate the bodies from the aircraft wreckage.
Probable Cause
The probable cause of the accident could be attributed to departure of the aircraft from controlled flight due to an external weather related phenomenon, mishandling of controls, spatial disorientation or a combination of the three.