DURING A POSTFLT DEBRIEFING; A DC10-10 CARGO PIC IS ALLEGED TO HAVE FALLEN ASLEEP FOR A 5 MIN PERIOD DURING CRUISE IN A NIGHT OP BY A JUMP SEAT FAA ACI. FLT ON FREQ WITH ZME; TN.

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WHEN FLYING NIGHTS ALL WK; THE FIRST NIGHT ESPECIALLY IS ONE OF ADJUSTMENT. NO MATTER HOW FRESH AND WELL RESTED ONE MAY SEEM TO BE EARLY IN THE EVENING; FROM MY EXPERIENCE; NATURAL BIORHYTHMS WILL CAUSE A WINDING DOWN PROCESS OF BODILY FUNCTIONS DURING THE PERIOD OF TIME THAT THE MIND/BODY IS NORMALLY AT REST. BEGINNING A SEQUENCE OF TRIPS FOR THE WK THAT WOULD OCCUR ON THE 'BACK SIDE OF THE CLOCK;' IE; FLYING ALL NIGHT; I WAS GOING THROUGH THE NORMAL CHALLENGES IN ADJUSTING TO THIS ABNORMAL SCHEDULE. THE SECOND HALF OF THE NIGHT FEATURED AN EARLY MORNING LAUNCH; AFTER HAVING HAD SEVERAL NIGHTS OF NORMAL SLEEP PATTERN. AN FAA INSPECTOR JOINED US FOR BOTH FLTS THAT EVENING. NATURALLY; ALL 4 OF US HAD TO WORK TO STAY AWAKE MUCH MORE SO ON THE SECOND FLT; WHICH DIDN'T BEGIN UNTIL EARLY MORNING. THERE WAS NOTABLY MUCH LESS DISCUSSION AND MOVEMENT IN THE COCKPIT IN CRUISE ON THIS LATER FLT. THE FLT DID PROCEED WELL WITH ATC AS USUAL; NOTHING DANGEROUS OR INAPPROPRIATE OCCURRED. ON DEBRIEF AFTER ARR; THE FAA INSPECTOR STATED THAT IT SEEMED TO HIM THAT FOR A PERIOD OF ABOUT 5 MINS IN CRUISE; I HADN'T MADE ANY MOVEMENTS. SO HE QUESTIONED ME ABOUT BEING ASLEEP. I ASSURED HIM THAT ALTHOUGH I NATURALLY FELT DROWSY; I DID NOT SUCCUMB TO SLEEP. I STILL RECOMMEND THAT A PLT FLYING ALL NIGHT WOULD BE WELL ADVISED TO PACE HIS ACTIVITY FOR MAX ALERTNESS DURING TERMINAL PHASES OF FLT TO UPHOLD SAFETY. THIS NECESSITATES ENERGY CONSERVATION DURING THE LESS CRITICAL (CRUISE) PORTION OF FLT. THE STUDIES THAT I'VE BEEN BRIEFED ON IN THIS AREA ALL POINT TO THIS SAME RECOMMENDATION. WHAT THE FAA INSPECTOR OBSERVED WAS THIS PHILOSOPHY IN ACTION. THIS MAXIM HAS SERVED ME SUCCESSFULLY DURING MY MANY YRS OF MOSTLY NIGHT FLYING. THIS FLT CAN BE ADDED TO THAT RECORD.