AMC 25.1305(a)(2) Fuel indication system(s)

ED Decision 2012/008/R

0.       Related references

AMC 25-11 Electronic Flight Deck Displays

1.       Purpose

This AMC provides guidance and means of compliance for demonstrating compliance with CS 25.1305(a)(2) when designing a fuel indication system(s).

2.       General objective

a.       The primary function of fuel indication system(s) is indicating the usable fuel quantity on board an aircraft. Additionally, the fuel indication system(s) provide(s) any alert and information to the flight crew to assist them in the task of managing the fuel quantity on board.

b.       Service experience indicates that scenarios leading to impending fuel starvation of one or more engines have developed into an unsafe system operating condition. Therefore, such scenarios have to be identified and, as required per CS 25.1309(c), appropriate information should be provided to the flight crew to enable them to take corrective action.

This information, including alerts, is provided in a timely manner so that any unsafe fuel starvation situation can be avoided.

c.       The fuel indication system(s) alerts as a minimum inform the flight crew of:

—         any abnormal fuel transfer;

—         a trapped fuel situation;

—         the existence of a fuel leak;

—         a low fuel level situation.

For each alert, corrective actions are made available to the flight crew. This should include for instance:

—                  procedure(s) to identify and isolate the fuel leak;

—                  procedure(s) to correct the abnormal fuel transfer and/or to manage the trapped fuel situation;

—                  diversion procedure or the instruction to land as soon as possible;

—                  any required procedure to avoid additional hazard (for instance: fuel coming into contact with wheel brakes during landing when a fuel leak is not isolated; exceeding centre of gravity or fuel imbalance limits).

3.       Usable fuel quantity

a.       The total usable fuel quantity is considered essential information. Operational regulations require the flight crew to regularly check the remaining total usable fuel quantity. This quantity is then evaluated when comparing the actual quantity of fuel used to the planned fuel consumption, and to ensure that sufficient fuel is available to complete the flight with the required fuel reserve. The total usable fuel quantity is therefore displayed full-time and it is easily and directly readable by the flight crew.

b.       As required per CS 25.1337(b), there is a means to indicate to the flight crew the usable fuel quantity in each fuel tank. It is considered acceptable that these individual tank quantities be only displayed when required. This may be displayed either at pilot discretion (on demand) or automatically as determined to support operational procedures associated with fuel system alerts.

4.       Abnormal fuel transfer between tanks

The fuel indication system(s) provide(s) any alert and information enabling identification of abnormal fuel transfer between tanks. 

Abnormal fuel transfer between tanks is a fuel transfer that - if no corrective action is taken - can lead to no fuel becoming available to an engine and/or fuel imbalance. This may result either from a fuel management system failure or from inappropriate flight crew action.

5.       Trapped fuel

The fuel indication system(s) provide(s) any alert and information enabling identification of trapped fuel situations.

Trapped fuel means any fuel quantity (above the unusable fuel quantity) gauged by the FQIS that cannot be supplied to the engine.

For instance, failure of an isolation valve in an auxiliary tank, failure of a transfer pump, fuel pipe failure inside a tank could result in trapped fuel. Also, inappropriate selection of fuel system configuration by the flight crew has to be considered.

6.       Fuel leaks

The fuel indication system(s) provide(s), as early as practical, any alert and information enabling the crew to identify a fuel leak.

Fuel leaks can be caused by a loss of integrity of the fuel system (for instance, fuel pipes failures, leakage of connections) and result in fuel being drained overboard the aircraft.

The fuel leaks analysis will identify all foreseeable leakage sources from the aircraft fuel tank(s) to the engine fuel nozzles. For the engines, it means that the effects of leaks upstream and downstream of the engine fuel flow meter have to be considered.

The leak detection may be performed by monitoring and comparing several sources of information (for instance fuel flows, fuel used computation, usable fuel quantities per tank(s) and total usable fuel on board before take-off).

7.       Low fuel level alert

a.       The fuel indication system(s) trigger(s) an alert in case of low fuel level. The low fuel level cockpit alert is applicable to any tank or collector cell that is not expected to be depleted in flight because otherwise this situation would lead to an engine fuel starvation. Fuel tanks that may normally be depleted during flight do not require a low fuel level alert.

b.       The alert is triggered when the quantity of usable fuel in the tank concerned reaches the quantity required to operate an engine for 30 minutes with the aircraft operated in optimum cruise conditions. When defining the 30 minutes under optimum cruise conditions the applicant will consider the mission profile for which the aircraft is designed.

c.       The safety analysis in accordance with CS 25.1309(b) and (c) includes as a minimum the following failure scenarios:

—         Erroneous high fuel quantity indication system (FQIS) readings;

—         Loss of FQIS gauging information.

No single failure of the FQIS (including total loss of FQIS power supply) or total loss of the primary basic FQIS information will lead to the fuel low level alert not being correctly triggered.

[Amdt 25/12]