How and why are the accessories of modern fighter jet engines oriented with respect to the airplane? Do the subsystems show up (see left image part) or down (see right image part)?

Jet engine accessories orientation

  • 4
    $\begingroup$ Wow classic homework question!! $\endgroup$
    – vasin1987
    Commented Dec 13, 2015 at 14:27
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    $\begingroup$ My first thought was "in the least convenient position for maintenance". I hope I'm wrong. $\endgroup$ Commented Dec 13, 2015 at 15:21
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    $\begingroup$ If you're downvoting because this looks like a homework question, please review this meta discussion first. We have no explicit policy on them and as some answers in meta say, even if a question is indeed for a test, good answers can still be interesting and helpful for other people. $\endgroup$
    – Pondlife
    Commented Dec 13, 2015 at 16:44

1 Answer 1


Engine Accessories On the Bottom

The engine looks like the General Electric GE F414, which is used (amongst others) in the Boeing F/A-18E/F Super Hornet and the Saab Gripen NG. In this case, the engine is mounted with the accessories below, i.e. in 6'O clock position. See this image:

Super Hornet Engine

An Aviation Machinist’s Mate (AD) performs maintenance on an F/A-18F Super Hornet. ADs are aircraft engine mechanics. They inspect, adjust, test, repair and overhaul aircraft engines and propellers. Image from americasnavy.tumblr.com

It is not correct that the engine accessories 'protrude below' the aircraft. The fusealge design is such that there are no protrusions, as can be seen in this image.

Engine Closeup

"US Navy 040708-N-9060G-009 Aviation Machinist's Mate 3rd Class Evonda Patterson, of Chicago, Ill., performs scheduled maintenance on the engine of an F-A-18E Super Hornet" by U.S. Navy photo by Photographer's Mate 3rd Class Michael Geary

Apparently, the reason for mounting the accessories down is for ease of maintenance as they can be accessed easily this way.
Other engines with the accessories on the bottom are e.g. the Pratt & Whitney F119 for the Lockheed Martin F-22 Raptor, the Eurojet EJ200 for the Eurofighter Typhoon and the SNECMA M88 for the Dassault Rafale.

Engine Accessories On Top

However, this varies from aircraft to aircraft, as evidenced by this Sukhoi Su-30MK with Saturn AL-31F(P) engines with the accessories on top.

Su 30 engine

Image from researchingaliensandufos.com


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