While we can speculate and debate endlessly, the crew at the controls would know the challenges they faced while diverting from Delhi to Lucknow airport on 15th July 2019. The flight which is typically 2 hours lasted 3 hours and 56 minutes and landed with 200kgs in tanks.
I have highlighted in my blogs and the same had been witnessed when Gatwick was shut down due to drone activity.
The Mumbai – Delhi Vistara A-320 Neo UK944 landed at Lucknow on 15th July after diverting, with about 6 minutes of fuel remaining. The aircraft would have departed Mumbai with the regulation fuel and possibly some extra fuel, looking at the forecast and actual poor weather at Delhi airport. Takeoff Mumbai 09:47 Z
Entered Hold 11:12Z at Delhi
Exited hold at 11:26 Z, hold time of 14 minutes.
The final approach at Delhi was carried out at 1150Z followed by a go around.
Arrived Lucknow at 12:40Z and landed at approx. 1320Z.
Following are the MET reports for Delhi, Jaipur and Lucknow
While it is futile to speculate at this moment, the facts will only be known post investigation. The initial diversion could be on account of strong tail winds or poor visibility associated with rain showers.
Lucknow had a forecast of rain and visibility decreasing to 1500m at the forecast time of arrival at Lucknow in the event of a diversion. The question arises is how much extra fuel did the crew uplift?
The interesting point I would like to highlight here is the route that the aircraft took to divert to Lucknow. While there would be sufficient fuel at the point the diversion was initiated from Delhi, typically fuel from Delhi to Lucknow and 30 minutes of fuel to hold over Lucknow. Ideally the aircraft would have landed at Lucknow with 30 minutes of fuel remaining in the tanks but in this case the aircraft landed with about 6 minutes of fuel left.
While the prevailing en-route weather shows widespread moderate to heavy rain , the reason why the crew took the aircraft south of Delhi towards Agra before turning left towards Lucknow airport. This flight path significantly increased the flight distance and the fuel burn. The blue lines represent the shortest diversion routes available to two closes alternates.
What should also be noted that west of Delhi was much clear of weather and airports like Jaipur, Udaipur could have been better choices. Its not known how much support the crew were getting from the airline IOC/Dispatch to form a correct picture of the available weather.
In 2014 Air India A-320 met with an accident after diverting from Delhi due low visibility and attempting to land at Jaipur which had prevailing low visibility too. Read final investigation report.
Operating to busy airports can be challenging with some unique situations that must be considered during the risk assessments. While all airlines consider the risk and uplift the additional for the flight getting into the busy airspace surrounding the airport, no airline considers the risks of getting out if a landing is not successful.
Additional fuel is carried for holding for poor weather or air traffic delays. Critical fuel as required by regulations, that of a missed approach segment is not carried by airlines and the regulator has failed to check the same in repeated audits.
While a diversion may be assumed a walk in he park, that of setting course to the chosen alternate airport, the difficulty of weaving out of the hair of other incoming and out going air traffic is not considered. This incident may help highlight similar issues if found relevant.