On 4 October 2017, a Airbus A320 (VT-ESE) being operated by Air India on a scheduled domestic passenger flight from Delhi to Surat as AI493 marginally overran the displaced threshold landing runway 22 at destination after an unstabilised approach in day VMC was followed by a late touchdown with insufficient distance remaining in which to stop. ATC were unaware of the overrun and it was not reported by the flight crew. None of the 151 occupants were injured and the aircraft was not damaged although several runway thresholds lights were. The return flight to Delhi was subsequently operated by the same flight crew.
The flight crew failed to report the overrun, advising ATC that the landing had been completed normally. The Captain then made a defect entry in the Aircraft Technical Log for “low braking action” which after checks was cleared by maintenance as “no fault found” and the aircraft was released to service. The crew then operated the aircraft on the scheduled return flight to Delhi and only when a subsequent inspection discovered damage to runway lighting was the overrun reported and an Investigation commenced by the Indian DGCA Office of the Director of Air Safety (Western Region) in accordance with the Aircraft (Investigation of Accidents and Incidents) Rules 2017. Data from DFDR were successfully downloaded but due to the delayed commencement of the Investigation, it was deemed that the relevant CVR data would have been overwritten and it was not downloaded.
It was noted that the 50 year-old Captain, who was acting as PF for the investigated flight, had a total of 12,683 hours flying experience which included 5,451 hours on type in command. He had held an A319/A320/A321 type rating for in excess of 12 years. The 38 year-old First Officer had a total of 375 hours flying experience, of which 125 hours were on type.
A NOTAM had been issued to alert pilots to the temporary displacement of the runway 22 threshold at Surat due to ongoing maintenance work which reduced the LDA to 1905 metres rather than the usual full length of 2,905 metres. The flight crew were aware that as the result of this, the usual ILS 22 approach was not available and that a non precision LOC-only 22 approach in accordance with a modified procedure would need to be flown. The surface wind was almost calm, the prevailing visibility was 5000 metres and the temperature was 25°C.
The AP was disconnected at a recorded 1,677 feet agl and the aircraft was subsequently configured for a full flap landing. In the presence of a slight tailwind component, the approach speed was found to have been above the applicable VAPP of 135 KIAS and, concurrently, the rate of descent was found to have been continuously above 1000 fpm until the aircraft reached 185 feet agl. These excesses were in breach of the stabilisation criteria to be met by 500 feet agl. As per the modified approach procedure, the aircraft should have been passing 840 feet agl at 2nm from touchdown but it was actually at 1,029 feet agl at that point. The flare was initiated by increasing pitch on reaching a height over the runway of 38 feet agl. The A/THR was disconnected at 20 feet agl and after 5 seconds in the flare, the pitch had reached 5.6° and the aircraft was floating over the runway at approximately 7 feet agl. Subsequently there were variations in pitch angle as the aircraft continued to float until, after 12 seconds in the flare, the aircraft touched down main gear first some 1300 metres beyond the displaced threshold.
The pre-selected speed brakes automatically deployed on touchdown, maximum manual braking was immediately commenced and reverse thrust selected and 12 seconds after touchdown, the aircraft had slowed to 15 knots and the low speed excursion followed which included a reversal of direction to backtrack as cleared.
An annotated representation of the landing roll. [Reproduced from the Official Report]
The Air India stabilised approach policy contained in the OM was found to state that “if an approach gets destabilised due to any significant deviation it must be stabilised (at the) latest by 1000 feet agl during an instrument approach, 500 feet agl during a visual approach or 300 feet agl during a circling approach”. It also stated that “if the above altitude limitation for stabilisation is not achieved (then) the pilot is required to carry out go-around”.
In respect of the defect entry relating to low braking action raised by the Captain after the flight, it was noted that no similar defects had been recorded in the 15 days prior to or after the incident sectors.
The Cause of the event was determined as “the aircraft continued landing after an unstabilised approach and a prolonged flare resulted in a delayed touchdown and subsequent runway excursion”.
Two Safety Recommendations were made as a result of the Investigation as follows:
- that Air India should reiterate the safety circular highlighting the incident and advising all crew to carry out a go around when an approach is not stabilised.
- That the DGCA HQ should take such other action is it seems fit with reference to the formally documented findings of the Investigation as to Cause.
The Final Report was completed on 5 November 2020 and published later the same month.