editorial_banner.jpg (54224 bytes)

Point of no return (PNR)

PNR definition:

The Point of no Return is the greatest distance that an aircraft can proceed past an airfield, and return to that airfield with the required reserve fuel still intact upon landing.

For multi-engined pressurised aircraft there are three types of PNR.

PNR Normal Ops: This assumes no loss of cabin pressure, and that the engines continue to supply

useful power, both out to the PNR and on the return journey to the airfield. In real life this is the most

common type of PNR, as modern turbine engines rarely fail, and cabin depressurisation is thankfully rare.

An example of a PNR Normal Ops scenario would be if the pilot was advised enroute that the destination airfield currently had a disabled aircraft blocking the runway. The pilot would calculate the last position enroute that would allow the flight to return to an airfield behind it, the weather at which was forecast to remain good, and the lighting was operating satisfactorily.

Nearing the PNR, the pilot would need to ascertain that the disabled aircraft had been removed from the runway, and the runway was again fully operational. If it was, then the flight could continue on to the destination as originally planned. If the runway had not been cleared by the time the flight reached the PNR, then the pilot would turn the aircraft around, and return to the planned alternate. Refer to Fig PNR 1.

1 Engine Inoperative PNR: This assumes normal operations out to the PNR, but that the aircraft may suffer

the loss of one of it’s engines and would in that case return to an airfield behind it. It is important to remember that you must use the Normal Ops TAS, flight level and winds out to the PNR, and the

1 Engine Inop TAS, flight level and winds back from the PNR in this case. As with all simple PNR’s, you may disregard all descents including descent to the 1 Engine Inop cruise level and descent into the airport you are returning to. As aircraft are normally less efficient with one engine shut-down, this means that, assuming the same reserve fuel is carried for all operations, the distance to the 1 Engine Inoperative PNR will be less than the Normal Ops PNR. Refer to Fig’s PNR 2 and 4.

Depressurised PNR: This assumes normal operations out to the PNR, but that the aircraft loses the

cabin pressure, and has to return to the alternate airport behind it at the Depressurised TAS, Flight Level

(typically FL130) and subject to the winds and temperatures at that level. Again, you may disregard all descents when calculating a “SIMPLE PNR”. Because aircraft (especially jet aircraft) are not at all fuel

efficient at low levels such as FL130, then assuming the same reserve fuel is carried as for normal and

1 Engine Inop operations, the distance to the Depressurised PNR will be the least of these three scenarios.

Refer to Fig’s PNR 3 and 4.

It should be noted that airline fuel policy normally states that different reserve fuel is carried for each of the

three scenarios. This is true in the Flight Planning portion of the ATPL exam when using either B727 or

B767 aircraft examples. In “SIMPLE PNR’s the question will quote a “safe endurance” which will already have the reserve fuel removed. This “safe endurance” may be regarded as “flight fuel” , all of which should be burned if you are to fly out to the absolute PNR.

“SIMPLE PNR’s” quote the safe endurance in minutes.
“COMPLEX” PNR’s associated with the B727 or B767 will quote a Fuel On Board (FOB) figure at a given position. The method used to find the particular PNR type when given FOB is different to these “SIMPLE PNR’s”.

COMPLEX PNR’s are covered in the “Flight Planning” Examination.

“SIMPLE PNR” Formula is Time to PNR =     Safe Endurance in Minutes x Groundspeed HOME
    Groundspeed OUT + Groundspeed HOME

This free training editorial is a sample taken from the Internet delivered ATPL Navigation course. It also features in a training book, called Navigation Part 1 (order reference Av2), which covers the ATPL syllabus topics of Airspeed, Altimetry, Equi-time Point, and PNR.

The book is available from Pilot Supply shops around Australia. A second editorial expanding on this one will follow in due course.

CLICK HERE for information on ATPL training books that are widely available.

CLICK HERE for information on ATPL distance learning via the Internet.



marty.jpg (10727 bytes)
Marty says ... "Goodbye to GA".

banner_lower.jpg (6878 bytes)