Originally Posted by
tdracer
Assuming the (now deleted post) was correct, and this is an issue with TCMA when combined with an unusual T/R application, it has nothing to do with reverse before being on the ground.
TCMA - Thrust Control Malfunction Accommodation - is something Boeing came up with to address an FAA (and later EASA) concern with Uncontrollable High Thrust (UHT) on the ground. UHT is nothing new - although uncommon (probability of occurance is somewhere between 1/10 million and 1/100 million flight hours), all turbine engine installations have failures that can cause the fuel metering valve to go wide open uncommanded. FADEC has made it less likely, but the potential failure is still there.
UHT was always assumed to be something the flight crew could address by shutting down the affected engine - but then there was an event on a 737-200. Going from memory here, but I think it was 1997, it was either in Egypt or an Egyptian operator (fuzzy memory on that part). Anyway, there was an issue with the JT8D fuel control where the splined shaft that fed N2 speed to the fuel control could wear excessively and start slipping. During takeoff power set, that spline started slipping - the fuel control thought the dropping N2 meant the engine was spooling down and opened the fuel metering valve wide open. The crew saw EGT spike over redlline and aborted the takeoff, but the fuel control didn't respond when they retarded the throttles. The went off the side at low speed - no one was seriously injured or killed, but it was a hull loss.
The FAA (and later EASA) decided this meant that UHT on the ground was catastrophic and therefore every aircraft/engine combination ever built didn't comply with the regulations (25.901(c) - no single failure shall result in an unsafe condition).
It become a long and quite messy story - the FAA ended up issuing partial exemptions for aircraft then in production, but dictated that we needed to address UHT on the ground for future aircraft certs. So starting with the 777-300ER/GE90-115B, Boeing came up with TCMA. In short, when on the ground, if the FADEC determines that the engine is at high power with the throttles at/near idle, and not decelerating, TCMA will shut the engine down. For what should be obvious reasons, TCMA is only active on ground, with quite robust air/ground logic that will default to air if it's not sure.
I wonder if this was the incident.
https://asn.flightsafety.org/wikibase/324400