This is a section from an Air Canada crew training document. It
describes some of the signals used during an interception when radio
contact cannot be established between interceptor and interceptee.
These signals are used to communicate mechanical problems with the
intercepted aircraft, and fuel status. It is referred to as the
HEFOE system for Hydralics, Electrics, Fuel,
"Flight crews should be familiar with the military HEFOE
signalling system. These standard hand signals permit the silent
communication of aircraft emergency system status to an intercepting
aircraft. The intercepting aircraft will initiate this communication
by formatting on the intercepted aircraft and placing a clenched
fist to his/her canopy. The intercepted aircraft responds in turn
with a clenched fist followed by the display of one to five fingers.
one finger for hydraulics, two for electrics, three for fuel, four
for oxygen and five for engine. In the case of fuel problem, the
intercepting aircraft can request your status by tipping an extended
thumb back towards his/her facemask. Your response would be one
clenched fist for each hour of fuel remaining and one finger for
each 10 minutes."