While carrying out an approach to land, I have always wondered about a scenario. If the departing aircraft ahead delays the takeoff. I continue my approach to the minimum decision altitude and see the aircraft still on the take off roll ahead. What is the latest point till which I can continue the approach. What if I go around straight ahead and the aircraft ahead lifts off below me? Is the safety compromised and if yes, how serious is it.
The final investigation report tells us what happened and which provisions of the regulations were not complied with. But the ‘why’ is still not known. Why did the three human groups fails to proactively participate in mitigating the risk is what needs to be investigated. The 4th human group which played a crucial role has not been investigated, the role of AI014. The human factor.
Interestingly, there was a bigger surprise awaiting when I read the report. Apparently, the Thai Airways aircraft was cleared for takeoff from Runway 29 at Delhi by the air traffic control. Even before the preceding aircraft AI014 had vacated the runway. Why did the investigators fail to notice this error?
AI014 vacated the runway at 18:23:24 UTC
THAI316 cleared for takeoff at 18:23:02-09 UTC
British Airways flight BAW143, aircraft B787-9, from London to New Delhi was given interception by Approach Radar Controller. The flight BAW143 established on ILS Rwy 29 at Delhi airport.
The inter arrival spacing between BAW143 and the preceding arrival, Air India Airbus 321 aircraft flight AIC014 was observed to 6.5 NM. The speed of preceding aircraft (AIC014) as 140 kts and succeeding aircraft (BAW 143) as 200 kts (with a speed differential of 60 kts)
The Aerodrome Controller without taking into consideration the speed of arriving BAW 143, the reduced inter arrival spacing and displaced threshold of RWY29 lined up and cleared the departing THA316 for CE2 intersection takeoff. The departing THA316 also took some time on the runway before commencing takeoff roll.
In the meantime, the arriving BAW143, which was approaching threshold of RWY29, initiated missed approach. Distance was less than 01 NM from touchdown [ approximately from the beginning of Rwy 29].
This simultaneous going around of the BAW143 and the departure of THA316 from Rwy 29 resulted in the breach of standard separation. The lateral and vertical separation was reduced to less than 01 NM and 200 feet respectively.
Radar positional image
Revealing statement but missed out
The above snapshot clearly states that the Thai316 lined up RWY29 and AI014 vacated the runway at 18:23:24 but the takeoff clearance was given at time 18:23:02-09. This procedural error was not highlighted in the report. Practically, this practice may be prevalent but from the human factor aspect, this reveals a tendency to take risks and/or inability to switch task to plan B of cancelling takeoff. Cognitive lockup takes place where the humans have a tendency of failure to switch tasks.( Read my paper on Cognitive lockup). A safe risk analysis and procedural modification is permitted. ICAO Doc 4444 allows reduced aircraft separation procedure after a risk analysis.
Separation of departing aircraft
A departing aircraft will not normally be permitted to commence take-off until the preceding departing aircraft has crossed the end of the runway-in-use or has started a turn or until all preceding landing aircraft are clear of the runway-in-use. Reduced separation is not yet permitted in India.
The takeoff roll commenced in the event of a rolling takeoff when the aircraft aligns with the runway centerline. The Thai aircraft was cleared for a rolling takeoff as per runway capacity enhancement procedures at Delhi airport.
ICAO DOC 4444, 184.108.40.206 When necessary or desirable, e.g. due to low visibility conditions, a landing or a taxiing aircraft may be instructed to report when a runway has been vacated. The report shall be made when the entire aircraft is beyond the relevant runway-holding position.
From an investigation and human factor point of view this is important. Remember, investigations are always done in black and white, there are no grey areas.
Unlike many airports which follow the reduced separation procedures as laid down in ICAO DOC 4444, following are the provisions at Delhi Airport.
- Pilot shall complete all mandatory pre-departure checks before entering the active runway for departure so that the aircraft is in a position to take off immediately upon receipt of take-off clearance.
- When the aircraft is issued with a line-up and takeoff clearance at the taxi holding position it shall be in a position to line up and affect an immediate take- off in one continuous movement.
- If the Controller observes a delay in respect of the departing aircraft commencing its take off run after issuance of take- off clearance, the take- off clearance will be cancelled and the aircraft be advised to vacate the runway immediately at the nearest taxiway to make way for the subsequent arrival or departure. Necessary entries in this regard shall be recorded in the Log Book.
- The nominal spacing between arrivals when there is a departure in between arrivals, is 7NM.
- Inter-alia states that “the spacing between two arrivals may be increased when the speed differential between the preceding and succeeding arrivals is high
The landing aircraft will not normally be permitted to cross the runway threshold on its final approach until the preceding departing aircraft has crossed the end of the runway-in-use, or has started a turn, or until all preceding landing aircraft are clear of the runway – in-use.
Probable cause as per the final report
Non adherence to SOP by the aerodrome controller
- The incident occurred at around midnight local time in India. The crew of the British Airways and Thai Airways aircraft would have been on a long haul flight. It would not be a time of circadian low for any of the three human groups but certainly fatigue and lethargy could have played a part in the chain of errors.
- The duty period of the ground based controllers could have been analysed to determine if they were at the fag end of their shift or just joined duty for the day. A human who is nearing the end of the work period is more likely to take risks since it marks completion of the job or task in hand.
- The controller probably knew of the close separation between the BA and AI aircrafts but decided to allow a heavy aircraft Thai316 to lineup and takeoff. Human factor analysis is critical in this situation of tight coupling.
- The Thai Aircraft had the option of not entering the runway if the crew were not fully prepared but they chose to do so. It could be a cultural issue of loosing face if told to stop or vacate the runway.