Las siglas QEC significan Quick engine change. En la página web que te indico abajo encontrarás más informació. Espero que te ayude.
Un saludo.

Jesús Garrido Muro. Traductor inglés - español

En el Diccionario aeronáutico, civil y militar (José Velasco Sales - Paraninfo) aparece esta traducción para QEC, es decir, quick engine change, que es un término común de mantenimiento en aeronáutica.

Gratas horas,

V

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Note added at 8 mins (2003-11-01 10:13:00 GMT)
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There was a QEC (Quick Engine Change) for the R-1830 on an A-frame at NAS Whidbey and in a couple of days we would be on our way again. But, we took a different route, and again did not make it to Kodiak.

http://www.daileyint.com/flying/flywar11.htm

By early June 1942, the first batch of 37 P-47B’s were issued to the 56th Fighter Group, with the 63rd Fighter Squadron being stationed at Republic’s Farmingdale airfield. One problem faced almost immediately involved the difficulty of changing engines on the B model Thunderbolts. Maintenance crews were finding this operation to be very time consuming. Republic responded with their first major change to the P-47 airframe. An 8-inch extension of the fuselage, forward of firewall allowed for a new Quick Engine Change (QEC) design that cut the time required to hang a new engine by better than 60%.

http://home.att.net/~historyzone/Seversky-Republic4.html

al español la gran mayoría de términos aeronáuticos, pues está establecido el inglés como idioma y estilo oficial de la aviación mudial.