... or did you mean an airport?
Yes, suitable overwater diversion airport.
This restriction was so that the airplane would have adequate electrical and pneumatic sources available in the event of a double engine failed situation...IE: same electrical/pneumatic redundancy as a four engine type, where an APU would not be approved for airbourne use (ala---B747).
The L1011 APU can be used (and is fully approved) , for both electrical and pneumatic sources, up to FL 310.
So, four engine redundancy, with a three engine airplane, with regard to electrics/pneumatics.
One should also remember...
no L1011 has ever crashed due to an aircraft/engine design defect...quite unlike the B747
or the DC10.
Lockheed TriStar, simply a superior design...make no mistake.
