A recent presentation given by the FAA (Intermixing of Cells in Nickel-Cadmium Batteries for Aircraft Usage) revealed the results of FAA testing on OEM and PMA battery cells.
The FAA found that intermixed OEM and PMA battery cells are just as safe and effective as original configuration batteries that are wholly composed of OEM cells.
The presentation was the result of an FAA study that successfully established that there are in fact no notable flight safety issues brought about by the intermixing of FAA-approved cells from different manufacturers.
Part of the reason that the FAA undertook this study is because of a statement made in an RTCA Standard DO-239 (“Minimum Operational Performance Standards for Traffic Information Service (TIS) Data Link Communications”) that the mixing of battery cells is a non-acceptable practice because of possible differences in capacities due to different designs, storage, and use or age histories. The FAA study found that this allegation was not accurate. The FAA’s findings are especially pertinent in the face of marketing assertions made by some battery manufacturers, who claim that the replacement of individual OEM cells with aftermarket PMA approved cells potentially leads to reduced battery performance or potential safety issues from cell intermixing.
The testing by the FAA Tech Center compared two configurations of Saft 4078-7 batteries. One configuration consisted of all OEM cells. The other configuration was half OEM cells and half PMA approved replacement cells. The tests that the FAA conducted included:
- Rated Capacity Test
- Charge Stability Test
- Duty Cycle Performance Test and
- Induced Destructive Overcharge Test
Experimental goals included determining the minimum capacity from the charged battery from the 1C rate to End Point voltage, establishing suitability of separator system during high temperature charging, gauging battery performance without maintenance over 100 duty cycles, and verifying safety in emergency situations.
This table shows an abbreviated summary of the results of the testing:
|Initial Rated Capacity||Rated Capacity at 122F||Repeated Rated Capacity||Induced Destructive Overcharge|
|OEM||44.7Ah||45.0Ah||45.3Ah||No flame or explosion|
|PMA||45.7Ah||46.3Ah||48.2Ah||No flame or explosion|
[i]Steve Summer- FAA, Intermixing of Cells in Nickel-Cadmium Batteries for Aircraft Usage, May 11, 2011.
The differences between OEM and intermixed batteries were very minor and they illustrated that it is perfectly feasible to mix OEM and FAA-PMA battery cells in a single battery within the expected parameters of the PMA approval – there was no evidence of adverse implications.
The FAA expects to release a report on the results of this study later this year.