Two incidents of aircraft declaring fuel emergencies on Thursday night and the diversion of 10 flights to Bengaluru have brought the fuel uplift policies of airlines into question.

On Thursday, a Jet Airways ATR (Madurai-Chennai flight) and an IndiGo Airbus A320 aircraft (Kolkata-Chennai) declared fuel emergencies, after being diverted to Bengaluru from Chennai due to runway closure. On the same night, an AirAsia Pune-Bengaluru flight was forced to land at the old HAL airport in Bengaluru (closed to regular airline movement since 2008) as reportedly, there was no room for parking at the Bengaluru airport. A total of 10 flights had been diverted from Chennai, owing to shortage of bays. The AirAsia flight did not declare a fuel emergency but could not be diverted to Chennai, as that airport was shut.

A Bengaluru airport spokesperson, however, denied there was a parking bay shortage. "We have 68 bays at the airport and those are sufficient," the spokesperson said.

A Jet Airways spokesperson said, "The incident is currently under investigation by the Directorate General of Civil Aviation (DGCA) and we are fully cooperating. As part of our active safety management, we seek to find ways to improve our operations in safety and efficiency. The investigation is ongoing. Our fuel policy is in line with DGCA requirements and industry best practices."

Jet Airways' fuel policy catered to the regulator's guidelines on minimum fuel requirements and the additional holding fuel, he added.

IndiGo said it was conducting an internal inquiry, adding the two pilots concerned had been taken off duty.

Last month, a Doha-Kochi Jet Airways flight landed at the Thiruvananthapuram airport with insufficient fuel.

DGCA regulations lay down the procedure for calculating the quantity of fuel required for each flight. These regulations are based on International Civil Aviation Organisation norms, according to which pilots are bound to declare a fuel emergency if an aircraft has fuel for only 30 minutes of flying time.

The regulations state the minimum fuel needed, while airlines periodically revise the flight fuel requirement. Jet Airways issues advisories to pilots on fuel uplift, based on fuel consumption on the route and past data on arrival delays. The flight commander is the final authority on the fuel quantity to be lifted for each flight.

Fuelling is done under the supervision of an engineer.

An IndiGo spokesperson said, "At IndiGo, we always carry the fuel equivalent or more than the amount stipulated by the DGCA. The past three months' fuel data dictate our fuel planning, according to existing conditions. It is a realistic value that meets all regulatory requirements."

The airline said its aircraft that had to eventually declare an emergency was carrying 1,200 kg of fuel in addition to the amount required under DGCA norms.

Airline fuel policies take into consideration fuel for diversions. Thus, for a flight between point A and B, an airline will carry fuel sufficient for the trip and landing at the destination (B), for a go-around, for an alternative airport (C), in case of diversion, and for holding for 30 minutes at C. Additionally, airlines are also required to carry contingency fuel, which is five per cent of the trip fuel (between A-B) or 200 kg, whichever is more. This is to provide for any additional fuel burn due to weather and wind conditions and the possibility of not being assigned an optimum flight level.

Airlines also carry extra fuel, factoring in the holding that might be required at the destination (B).

But sources say airlines have different policies on carrying extra holding fuel for the destination and some airlines carry this additional fuel only when flying to congested airports, not for all flights.

Typically, airlines do not carry fuel far in excess of the stipulated requirement, as it adds to aircraft weight and increases fuel burn.

"At AirAsia India, we carry additional fuel on sectors that burn more than the planned amount due to air traffic control or flight restrictions. This is based on data analysis to ensure the contingency fuel of five per cent is not utilised other than in unforeseen circumstances that occur after take-off," said the airline's managing director, Mittu Chandilya.