Vistara lands with “Mayday Fuel”situation, challenges of diversion

 

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.

  • Airlines are not carrying the mandatory fuel to cover the completed go-around procedure
  • Diverting from a busy airport/airspace can practically take additional time and fuel since the air traffic controller needs to separate the diverting aircraft vertically and laterally/longitudinally from the 40-50 other aircraft in the airspace.
  • Choice of available alternates dwindle fast in the event of poor weather or mass diversions due to unavailability of parking space at alternates.
  • A direct flight as the crow flies may not be available. The safety risk assessment while formulating the fuel policy must address these points.
  • The regulator who approves the fuel policy must accept the risk post approval.

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

Screen Shot 2019-07-16 at 10.46.09 AM.png
Delhi Met report
Screen Shot 2019-07-16 at 10.45.40 AM.png
Jaipur Met report
Lucknow weather forecast and actual

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 weather

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.

Flight Path

Flight path VS direct line (blue) to Jaipur & Lucknow
Satellite weather image

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.

Past accident due low fuel

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.

Air India accident Jaipur 2014

mindFly analysis

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.

With increasing complexity of airspace reserve fuel must be increased.

Allowed to touchdown late but not as per calculations

 

It may sound too simplistic but from a conservative point of view, after touch down the aircraft should be stoppable within the physical proximities of the runway. The current landing distance calculations are based on a touchdown within the first 1500ft but the touchdown zone markings extend till 3000′ on a typical runway.

Contributory causes

The pilot is allowed to touchdown latest by 3000′ on a runway length 7800′ and above leaving a distance of 4800′ in a worst case scenario. A risk based safety margin must be adopted by the operators especially considering the long landing distance data.

Landing distance

Actual Landing Distance

Flight Test Conditions


(1) The braking coefficient of friction obtained from not less than six landing tests conducted in accordance with FA.R 5 25.125 and subject to the additional provisions listed below should be used to establish the ground
braking distances.
(i} The landing should be preceded by a stabilized approach not to exceed an angle of 3° down to the 50-foot height and at a calibrated airspeed not less than 1.4 Vso (stall speed)·
(ii) The average touchdown rate of descent should not exceed 6 feet per second. Longitudinal control and braking application procedures must be such that they can be consistently applied to yield a nose gear touchdown
rate of descent that does not exceed 8 feet per second.
(iii} The runway should be level, smooth, hard-surfaced, and
well-soaked.

Touchdown Zone

European Action Plan for the Prevention of Runway Excursions – Released Edition 1.0 – January 2013 reveals the following:

The parameters affecting the landing distance are published in the Flight Operations Manual. Flight crew should have a good understanding of the sensitivity of the landing distance to these parameters in order to make
sound go-around decisions. The following data shows the effect of relatively minor deviations from a baseline calculation of landing distance for a wet runway. The reference condition is a reasonably attainable performance level following normal operational practices on a nominal wet
runway surface. The reference QRH data on the bar chart below is based on:
1500 foot touchdown
VAPP=VREF+5, 5 knot speed bleed off to touchdown
Sea Level, Standard Day (15 C)
No wind, no slope
Recommended all engine reverse thrust
Braking Action – Good, consistent with FAA wheel braking definition of a wet non-grooved runway.
The vertical line represents the dispatch requirement that is 1.92 times the dry runway capability of the aeroplane.

European action plan Version 1

Read More

FAA issues safety alert, you need extra safety margin for landing on wet runway

 

The recent spate of runway excursions at Indian airports may have multiple contributory causes including but not limited to :

  1. Piloting technique
  2. Tail winds
  3. Runway condition wet/contaminated
  4. Runway friction level
  5. Psychological pressures

The pilots are required to calculate the landing distance of the aircraft based on the aircraft condition , environmental factors and runway conditions. After the calculation there is a 15% safety margin added to cater for various inaccuracies.

FAA has issued a safety alert for operators SAFO19003. As per FAA several recent runway-landing incidents/accidents have raised concerns with wet runway stopping performance assumptions. Analysis of the stopping data from these incidents/accidents indicates the braking coefficient of friction in each case was significantly lower than expected for a wet runway. These incidents/accidents occurred on both grooved and un-grooved runways. The data indicates that applying a 15% safety margin to wet runway time-of-arrival advisory data, as recommended earlier.

These overruns have occurred on grooved and smooth runways during periods of moderate to heavy rain. Analysis of these incidents/accidents indicates that the braking coefficient of friction in each case was significantly lower than expected, and that 30 to 40 percent of additional stopping distance may be required if the runway transitions from wet to contaminated based on the rainfall intensity or reported water contamination (greater than 1/8-inch depth). For the operational in-flight landing assessment, determining whether the runway is wet or potentially contaminated is the pilot’s responsibility.

Airports like Mumbai , Kochi, Kozhikode where there is heavy rainfall during monsoons and accompanied with tail winds, the runway becomes contaminated. In the absence of runway condition reporting process and the possibility of sudden heavy shower, the crew needs to  calculate landing distance performance for contaminated runway with margins more than 15% as currently used. Rubber deposits further increase the risk of poor braking.

From 2020 ICAO will change the definition of damp runway to be considered as wet. As an immediate risk mitigation action, operators must asses the risk as per the SMS program and consider increasing the safety margin for wet runway beyond the current 15%.

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