You may have also noticed on some aircraft (usually the 727's), the caterer's used to put an engine cover (plug type) to prevent FOD from entering the engine off the catering truck when pulled up to the aft service door.
Engine covers are put on for a variety of reasons with each airline having different standards as to when they are installed. Some cargo carriers (since their aircraft sit for extended periods during the weekends, routinely cover their engines during this extended down time.
Additionally, many carriers utilize pitot tube and static port covers, to prevent small livestock (bugs) from making homes in the tubes & ports (which would cause a loss of Air Data Instrumentation - Airspeed, Altitude and Static Air Temp).
Freight Dogs Anonymous - O.O.T.S.K.
DAMN! This SUCKS! I just had to go to the next higher age bracket in my profile! :-(