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Fuel - In-Flight Management (Normal Operations)

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Category: General General
Content source: SKYbrary About SKYbrary
Content control: EUROCONTROL EUROCONTROL

Description

In-flight fuel management encompasses pilot responsibilities for verification, utilization, monitoring, recording and reconciliation of the fuel loaded on the aircraft. The concept of in-flight fuel management includes ground operations with intent to fly so any and all fuel considerations while on the ground or fuel consumed during ground operations (pre-takeoff and post-landing) are, by definition, included as a facet of in-flight fuel management.

Threats

The principle threats to effective in-flight fuel management are complacency, failure to comply with Company policy and intentional deviation from the planned flight profile. The effects of poor in-flight fuel management can be broadly divided into three primary categories. These categories are Operational, Legal and Financial.

Effects

Operational

Poor in-flight fuel management can lead to the requirement to return to the gate for more fuel, the need to change the preferred alternate to a closer one to remain legal or even the neccessity to make an enroute diversion to a new destination to refuel. While none of these effects are inherently dangerous, they all represent the inability to complete the flight as planned and have the potential to cause schedule disruptions. Complacency could result in the late determination of a fuel leak whereas intentional deviation from the planned flight profile could result in fuel consumption well beyond that anticipated. In the worst case, poor in-flight fuel management can lead to fuel exhaustion and forced landing with the potential of the loss of aircraft and loss of life.

Legal

Regulations dictate the minimum amount of fuel required for a given flight profile. Both regulations and Company policy dictate actions to be taken when fuel available is not sufficient to continue the flight as planned or when fuel reaches certain pre-defined values. Failure to comply with these regulations can lead to enforcement action and to the potential of administrative action (suspension of AOC, loss of licence, etc) or financial penalties being assessed against the pilot, the Company or both.

Financial

For most aviation companies, fuel is the single largest expenditure. Poor in-flight fuel management can result in inefficient use of the available fuel leading to higher consumption and increased cost. In flight diversion induced by poor management or misuse of the available fuel will result in significant additional costs due to the expenses incurred as a result of the diversion as well as the costs associated with the resulting schedule disruptions. Should inappropriate in-flight fuel management result in enforcement action by the National Aviation Authority (NAA), the potential fines and penalties can present an additional financial burden to the company.

Defences

As stated above, in-flight fuel management encompasses verification, utilization, monitoring, recording and reconciliation of the fuel loaded on the aircraft. At all stages of flight, the flight crew must be vigilant regarding their fuel state and, to the maximum extent possible, adhere to Company policies and fly the planned profile. The following, based on phase of flight, is offered as guidance for appropriate in-flight fuel management.

Pre-start

  • Is the fuel on board the aircraft sufficient for flight?
  • Has the requested amount of fuel actually been loaded on the aircraft?
  • Has the uplift been verified (fuel on board minus fuel remaining from the previous leg should equal the fuel loaded)?
  • If there is a fuel uplift discrepancy, it must be reconciled before flight as a discrepancy could indicate a fuel gauge error.
  • Are ground services (power and airconditioning) available or is an early APU start required? If an early APU start is necessary, has that fuel burn been considered in the total fuel requirements.
  • Are there known departure delays that could result in utilizing more than the fuel amount planned for ground operations?
  • Is de-icing required? If de-icing is done at a remote location or as an 'engines running" profile, has the additional fuel been accounted for as part of the total consumption on the flight plan?
  • Is the final payload greater than the planned load? If so, additional fuel may be required.
  • Has the aircraft been loaded properly? In most aircraft, a forward Centre of Mass will result in a higher fuel burn.

Start and Taxi

  • How long/far is the pushback procedure? If there is a significant time involved in the push, engine start should be delayed until close to or reaching the tug disconnection position to conserve fuel.
  • Does Company policy allow for taxi with less than all engines running? In cases where there is likely to be an extended time between pushback and takeoff, taxi with less than all engines operating can result in a reduced per minute fuel burn allowing for a greater period of time before all taxi fuel is consumed. Engines must be started in time to comply with the manufacturer limitations on minimum warm up period prior to application of takeoff power/thrust.
  • In the event of an assigned delay after taxi has commenced, what is the required minimum brake release fuel? Is it possible to stop the aircraft and shut down some or all of the engines? Do the regulations and Company policy allow for consumption of any or all of the route reserve while on the ground? Is it possible to change the flight profile (speed, altitude, route or alternate) to reduce the minimum brake release fuel? If it becomes apparent that the flight will not commence the takeoff roll with the minimum legal fuel amount remaining, it must return to the gate for more fuel.

Takeoff

  • Is a derated or reduced thrust takeoff appropriate?
  • Are the optimum flap setting and V speeds for the runway and aircraft weight being utilized?
  • What is the aerodrome minimum thrust reduction altitude? Does Company policy allow for thrust reduction at that altitude?
  • If takeoff direction is opposite to that of the route of flight, do ATC restrictions allow for reduced forward speed and increased rate of climb to minimize the distance traveled while heading in the wrong direction and allow the turn towards track to be accomplished earlier?

The takeoff is a high power / high fuel flow event. Optimizing the thrust, flap and thrust reduction/acceleration profile will have a positive effect on reducing the amount of fuel burned.

Climb

  • Where possible, an uninterupted climb at the flight plan climb speed is the optimum profile. Deviation for terrain, weather or ATC restriction may be necessary.
  • Climb at the planned speed or cost index. Climbing at a higher speed will result in a higher burn during the climb phase. If the climb is interupted due to ATC restrictions, consider reducing airspeed during the level segment and subsequent climb to reduce the fuel penalty caused by the level off.
  • When practical during the climb, do a quick fuel calculation to confirm that there are no fuel leaks. Fuel burned plus fuel remaining should approximate the original fuel load.
  • Approaching planned cruising altitude, crosscheck the actual aircraft weight and temperature deviation against those on the flight plan? If they are significantly different, an adjustment to cruising altitude might be necessary.

Cruise

  • Reaching top of climb, conduct a more accurate fuel leak check.
  • Compare actual weight, temperature and wind to that on the flight plan and adjust cruise profile as appropriate.
  • At the first flightplan waypoint after top of climb, record actual fuel remaining and compare the amount with the flightplan. Repeat at the Company specified interval.
  • If the fuel trend is negative, adjust the flight profile early. Changes in speed, altitude or route will have the greatest overall effect if done as soon as possible. If fuel trend continues to be negative, consider changing the alternate to a closer aerodrome.
  • If the planned cruising altitude is not available, adjust the speed/cost index at the assigned altitude in accordance with manufacturer/Company recommendations to minimize any additional fuel burn.
  • Follow the planned vertical profile step climbing when appropriate. The timing of these climbs should be adjusted to compensate for differences between planned and actual weight and temperature.
  • If the fuel state becomes such that continuation of the flight is no longer prudent or legal, or might become so if the current fuel trend continues, make the diversion decision early. This could be a progressive decision such as "if the fuel remaining at point "Y" is XXXX or greater, I will continue towards destination, if it is less than that amount, I will divert to YYYY". Reassess the diversion decision and profile as often as necessary until it has been determined that flight to the planned destination is achieveable with the fuel remaining or that a diversion is a requirement.
  • Approaching the top of descent point, pilots should be satisfied that they have at least the legal minimum fuel required to continue to their destination.

Descent

  • From a fuel use perspective, the optimum descent point is one that would allow for continuous descent with thrust at idle from commencement of descent until reaching approximately 300 to 500 meters above ground on the approach to the landing runway. The realities of conflicting traffic, approach routings, noise abatement criteria and ATC restrictions make the profile difficult to achieve but pilots should strive to come as close as they can.
  • Where possible, planning to descend at a reduced airspeed will result in an earlier top of descent and a reduction in fuel consumption. Obviously, if the reduced airspeed does not meet ATC requirements, the earlier descent point would then necessitate a descent with thrust above idle to meet the speed restrictions and result in a higher overall fuel consumption.

Holding

  • Where possible, the likelihood of a holding requirement should be determined in advance. Wtih appropriate ATC approval, this might allow the pilot to reduce the aircraft forward speed thus reducing or even eliminating the time in the hold. This will also result in a lower overall fuel consumption.
  • When a hold clearance is issued, the pilot must confirm that there is sufficient fuel on board to allow him to hold until the issued expected further clearance time (EFC) and still have the required fuel to conduct the approach, missed approach and diversion legally. If there is insufficient fuel, the holding clearance should be refused unless a more favourable EFC can be negotiated.
  • If estimated holding delays exceed the fuel available, a diversion time should be calculated based on the time that fuel would be depleated to the minimum required for diversion based on flight from the holding location to the diversion aerodrome plus final reserve fuel. The pilot can elect to divert immediately or can hold in hopes that the delay will be less than anticipated. However, diversion must be initiated when fuel remaining reaches the calculated diversion requirements.

Approach

  • A continuous descent transition to the approach and a minimum drag configuration for initial approach is the most fuel efficient profile if traffic and ATC restrictions allow.
  • Maintain the aircraft in clean configuration for as long as practical.
  • Where conditions and company policy allow, use a reduced final flap setting for the approach.

Landing

  • Where appropriate, reduced flap landings are the most fuel efficient.
  • Similarily, where appropriate, use of idle reverse instead of full reverse thrust can result in a fuel savings although can also result in correspondingly higher brake wear.

Taxi

  • If Company policy and conditions permit, taxi procedures with less than all engines running will conserve fuel.
  • Delay APU start as long as possible and minimise APU use by switching to ground services as soon as they are available.

Typical Scenarios

  • The pilot of a privately registered single engine aircraft made a request to the aerodrome fuel company for preflight refueling. An uplift of 30 litres per tank was requested. The request was misunderstood by the refueler and instead of adding 30 litres to each of the two tanks, he added a total of 30 litres split between the tanks. The charge for the fuel was added to the aircraft owner's account but the owner did not reconcile the actual uplift against the amount requested. The aircraft then departed on a cross country flight. Two hours after departure, the left tank ran dry followed shortly thereafter by fuel exhaustion of the right tank. The pilot carried out a forced landing into a field which resulted in the collapse of the nose landing gear and damage to the propeller and engine. There were no injuries.
  • In an effort to get back onto the published schedule following a 30 minute departure delay, the captain of an A320 elected to cruise at FL320/M.79 instead of the planned profile of FL360/M.76. Approaching the top of descent point, it was determined that all extra fuel inclusive of the route reserve had been utilised and that the aircraft would no longer have legal diversion fuel remaining at the destination runway missed approach point. The weather at destination was VFR so the captain elected to continue. An emergency situation at the destination airfield resulted in a 15 minute landing delay during which time the captain determined that he would be landing with less than final reserve fuel remaining. A MAYDAY - fuel was transmitted and the aircraft landed at the planned destination on a priority basis. The National Aviation Authorities are investigating the occurence with possible enforcement action against the captain pending.

Solutions

In-flight fuel management is an acquired skill requiring situational awareness, discipline and compliance with both National regulations and Company policy. To be effective, careful preflight fuel planning must be followed by a concerted effort to utilize the fuel as planned during all phases of flight.

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Further Reading

ATSB