Ernest K. Gann’s novel/screenplay The High and the Mighty (1954) sensationalized a peril of crew (and passengers!) after a mechanical mishap on a trans-Pacific flight. The theme of the movie introduced we laypeople audience to the dramatized concept Hollywood named: The Point of No Return — when to turn back or commit to journey onward.

Today’s arithmetic has the benefit of digital calculation. No longer are there margins of error induced by the width of pencil lead on paper chart. It behooves a pilot to maintain an awareness of where he is and specific to this discussion, a safe path to alternative landing [at a suitable airport] should the trip need to end prematurely. Our pre-flight planning analysis arms us with reliable forethought to avoid reliance upon gut instinct or seat of pants.

Note: With a single engine aircraft a diversion could be an open field or stretch of road that gliding distance will allow. So, you as pilot are always reliant upon senses of judgment. Good Luck, we're all counting on you. 

A high flying jet however will have options. Over water operations is more problematic but the objective is to; always have a successful outcome. A line for decision may be more comprehensible as a measured distance but is more a function of timing. The fact is; it is not called Point of No Return… rather; Equal Time Point (ETP). This is the precise moment where it takes the same amount of time to u-turn so to speak or press forward. Not displayed but accounted for are winds and temperature conditions at cruising altitude. Consider that it may be a shorter measured distance one direction mileage wise but if facing stiff opposing winds aloft it may take longer to fly them. A longer distance mileage wise might be flown more rapidly then that of the shorter with tailwinds. So, there is a computed point in time where a logical decision is reached.

There can be multiple on a long over-water route. On a recent 10+ hour hop we plotted 4 ETPs. Actually 12. Within each of the 4 groupings are 3 types. DEPRESS (depressurization), 1ENGINE (loss of engine), and MEDICAL (onboard medical emergency). Observe the dispatch release beginning with ETP 1 through 4 below:

The second box, highlighted group, ETP2, contains two airports deemed suitable. In this case: PACD (Cold Bay Airport) in the Aleutians and PMDY (Henderson Field) on Midway Atoll. As you surmise these are in the middle of ‘nowhere’, beyond mainland US and short of our intended final destination. These alternates will change as we progress and thus there are subsequent ETP groupings.

Loss of cabin pressurization is a critical one. At these high altitudes one can’t function physiologically for very long without supplemental O². An immediate decent to an altitude deemed survivable is necessary. 15,000 feet is the generally accepted. Unfortunately doing so will double the rate of aircraft fuel consumption. Jets fly the icy upper levels for reasons of speed and economy. When forced to fly in the dense lower atmosphere efficiency is lost and whereas we planned for optimum fuel now we will end up short. Thus, the need for an escape plan. There is not enough fuel to continue on oblivious so as we are decending we are also questioning our route. Have we reached our ETP?

I plotted ETP(s) on a digital chart for easy reference in-flight. See the screen-grab below:

Observe DEP2, a plotted waypoint along this westbound (the blue line) route. It is located using Latitude and Longitude. A (black) arrow line vector shows the approximate direction to turn. PACD is a right turn to roughly North and, if past the DEP2 waypoint, PMDY will be found to the South West. These alternate airports are already pre-loaded into the box (nav system) so a route change can be actuated quickly with a button press or two and crew confirmation.

A curious eye will see ? 37N160 in chart center and also 0730z atop a magenta flag marker. The latter is known as a “10 minute check” — a timed event. The label is 07:30 UTC along with an actual lat/lon position report and is created enroute to compare with the plotted route. It serves as a reality check for navigational compliance accuracy. It is noted 10 minutes after passing the previous fix which depicted in shorthand is at North 37 degrees 160 West.

Armed with computerized clarity we are less vulnerable and don’t face the dilemma that our performers faced on the silver screen. Great aviation movie classic BTW and — spoiler alert — our High and the Mighty live happily ever after.