OPNLguy From , joined Dec 1969, posts, RR: Reply 1, posted (13 years 1 month 1 week 1 day 5 hours ago) and read 796 times:
If you are refering to what looks like a 1/4" female recepticle (like those used for older stero headphones), those are located at various locations on the aircraft, Boeings, at least, and are part of the service interphone system. They allow the mechanics to communicate with the cockpit (usually with another mechanic there) in troubleshooting, calibrating, or repairing some types of problems during servicing.
As far as the ones near the engines are concerned, "trimming" an engine would be a good example of how they're used. The engine must be run, and one mechanic tweaks the fuel control unit settings at the engine, while another in the cockpit reports various engine settings.
Buzz From United States of America, joined Nov 1999, 697 posts, RR: 23 Reply 2, posted (13 years 1 month 1 week 12 hours ago) and read 769 times:
Hi Joge, Buzz here. Yes, that's a place to plug in a headset cord. And it's not bad for some things. But it's close enough to the inlet to kill you if you use it ona running engine. I've often wondered why Douglas and Airbus put them there. On 737's and 757's it's back in the fuselage, so nothing gets eaten by the engine.