AMC
25.981(b)(1) Fuel tank flammability design precautions
ED Decision 2009/010/R
The intention of this requirement is to introduce design precautions, to avoid unnecessary increases in fuel tank flammability. These precautions should ensure:
(i) no large net heat sources going into the tank,
(ii) no unnecessary spraying, sloshing or creation of fuel mist,
(iii) minimization of any other energy transfer such as HIRF;
Applicants should limit the heat inputs to the maximum extent. Heat sources can be other systems, but also include environmental conditions such as solar radiation. The following design features have been found acceptable:
— heat insulation between a fuel tank and an adjacent heat source (typically ECS packs),
— forced ventilation around a fuel tank,
— fuel transfer logic leaving sufficient fuel in transfer tanks exposed to solar radiations on the ground in order to limit their effects
— heat rejecting paintings or solar energy reflecting paints to limit the heat input by solar radiation.
A critical parameter is the maximum temperature rise in any part of the tank under warm day conditions during a 4 hours ground operation. Any physical phenomenon, including environmental conditions such as solar radiation, should be taken into account. A temperature increase in the order of 20°C limit has been found acceptable for tanks not fitted with an active Flammability Reduction Means and therefore unable to meet the exposure criteria as defined in M25.1(b)(1).
Note 1: for tanks fitted with Flammability Reduction Means, applicants should limit heat and energy transfers to the maximum extent. No maximum temperature increase limit is defined; however the 20 °C limit is applicable in case of dispatch with the active Flammability Reduction Means inoperative.
Note 2: the maximum temperature increase under the conditions described above should be quantified whether or not the affected tank is fitted with a Flammability Reduction Means.
[Amdt 25/6]
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