180 km into Pakistan: Indigo flight's request to skirt storm denied

On May 21, passengers on board the Delhi-Srinagar Indigo airlines flight encountered a grave threat to their lives due to a series of miscalculations, including the decision to fly into a hailstorm en route to Srinagar. The beleaguered flight, with several of its flight-aiding instruments malfunctioning, landed at Srinagar with the assistance of Indian Air Force (IAF) controllers on the ground, who advised the pilots on the plane’s altitude and speed using data from IAF’s radars designed to track planes and aerial threats.

The incident began when Indigo flight 6E-2142 was flying just north of Pathankot in Punjab. The pilots contacted the IAF’s Northern Area Control at Udhampur in Jammu and Kashmir, requesting permission to divert approximately 180 km west into Pakistan to skirt around the approaching storm. However, the IAF team at Udhampur refused permission, citing that the authority to approve a route change lay with the air traffic controllers at New Delhi. The Indigo crew was also advised about a notice to airmen (NOTAM) issued by Pakistan last month, barring Indian-owned airliners from overflying Pakistan.

According to sources, the passenger flight’s crew was assisted in coordinating their route diversion by contacting Delhi Area Control and obtaining the requisite contact frequencies for Lahore Control to request overflight clearance for weather diversion. However, Lahore ATC refused overflight clearance, and the aircraft proceeded towards Srinagar.

The Indigo flight, an Airbus A321 Neo, is equipped with a built-in Doppler weather radar. The Directorate General of Civil Aviation (DGCA) has ordered a probe to investigate why the pilots chose to fly into the hailstorm instead of diverting to Amritsar or Pathankot after being refused permission to fly westwards.

Once the aircraft entered the hailstorm, the pilots faced a potentially life-threatening situation, encountering severe turbulence and huge variations in airspeed. The plane descended at 8,500 ft per minute at one point, exceeding the typical 1,500–2,000 ft per minute for a standard approach.

The on-board sensors indicating speed and altitude, both crucial for landing, were not functioning. This is known in aviation parlance as the ‘angle of attack’ sensor, which likely failed due to hail or ice, resulting in speed and altitude errors. The Airbus A321’s fly-by-wire system has a backup that requires direct control from the pilots.

Due to poor visibility, the IAF ground controllers at Srinagar used high-tech radar capable of tracking the speed and altitude of aircraft. The Indigo pilots were provided with readings of their speed and altitude, enabling them to land safely. Fortunately, the passengers had a narrow escape, and although the nose of the plane was damaged due to the hailstorm, a potential disaster was averted.