Critical Pts & Pts of No ReturnATC Chapter 5

Aim

To identify operational considerations for flight planning, and demonstrate the use of calculating

Critical Points & Points of No-Return

Objectives

1. Define the Critical Point2. Demonstrate method of Critical Point3. Define the Point of No-Return 4. Demonstrate method of PNR5. Summary of the above

1. Define Critical PointWhat is a Critical Point?

Also known as Equi-Time Point - ETP

It is the point between departure & destination where it would take the same amount of time to proceed to destination or turn back.

DestinationDeparture

45min 45min

Critical Point

In nil wind where would the critical point be?In the middle!

If there is wind, this will move the critical point into wind.

1. Define Critical PointWhat is a Critical Point?

The equation for the critical point is:

Remember, ground speed will be affected with wind. Calculations for accurate ground speeds out & back must be calculated.

DestinationDeparture

GS Home GS OUT

Critical Point

Total Distance

1. Define Critical PointHow is the CP derived?

The CP is the point where;

, where DB = Dtotal – DA

multiply both sides by Shome & Sout

2. Use of the CPMethod

Flying from YPPF to YMIATotal distance is 210nm20kt tail wind outbound from YPPF to YMIATAS = 120kts

YMIAYPPF

GS Home = 100 kt

Critical Point = 87.5nm from YPPF

Total Distance = 210

GS out = 140 kt

2. Use of the CPWhen can we use this?• Flights over water• Flights in remote areas • Long distance flights • Diversions due to weather• Increase in situational awareness

3. Define the PNRWhat is the Point of No-Return?

Also known as PNR, it is the point where there is insufficient fuel to return to departure aerodrome with reserves infact.

The calculation is crucial on flights where aerodromes are limited such as remote areas or water

destinationdeparture PNR

Beyond this point, if the aircraft turns back it will not be able to land with reserves infact

3. Define the PNRConsiderations?• The PNR is independent of the CP, as PNR is fuel consideration.

• The PNR will always be beyond the CP, because at the CP there must be fuel to either proceed or return, this is not the case with the PNR

• Any wind will reduce the dist to the PNR as in a tailwind due extra fuel burn to return, and in a headwind due extra fuel burn to go against wind

destinationdeparture PNRCP

3. Define the PNRHow is the PNR derived?

The PNR is the point where;

where THome = Endurance Available – TOUT

4. Demonstrating PNRPlanning method

The Endurance is the amount of flight time left after having subtracted reserves, holding, taxi.

Eg: 590 Lt total, 90lt FR, 15lt taxi, 0Lt holding, variable reserve 15% Total Fuel AVAILABLE for flight = 421 Litres to use for a PNR, @ 100lt/hr = 4.2hours

If TAS is 180kts, wind is 20kt tailwind outbound, fuel flow is 100lt/hr how long will it take to reach the PNR?

With the above, how many nautical miles is the PNR from departure?

Distance to PNR = 1.87 hrs X 200 kts outbound = 374 nm

destinationdeparture PNR

GS out =200kt

GS home =160ktWind +20kts tail

4. Demonstrating PNRPractical method

The previous example is useful for planning purposes. However this is not always the case for ‘actual flight’

Why is this?• Fuel flows may change depending on the operations

o Eg: If the pilot changes cruise settings, altitudes due unexpected weather, go arounds, the overall fuel flows will be different!

Eg: Flying at 180kts, with 20kts tailwind outbound, fuel available for PNR = 340 Lt, fuel flow 100lt/hr

Therefore, for every ground nautical mile flown, the aircraft burns 0.5 litres outbound

4. Demonstrating PNRPractical method – Engine failure

Eg: Outbound TAS = 180kts, fuel flow 100lt/hr, total fuel 500lt, wind 30kts headwind outboundEngine failure TAS = 120kts, fuel flow 60lt/hr

How far from departure is the PNR?

Fuel available for PNR = 500 – 90rsv – 15taxi – 15%vbr = 343 Litres

from departure

destinationdeparture PNR

GS out =150kt

GS home =150kt

Wind – 30kts head

4. Demonstrating PNRPractical method – Climbing considerations

If climbing, take into account the fuel used in climb/descent.

Eg: Outbound TAS = 180kts, fuel flow 100lt/hr, total fuel 516lt, wind 30kts tailwind outboundEngine failure TAS = 120kts, fuel flow 60lt/hr Climb fuel = 20lt & 35nmHow far from departure is the PNR?

Fuel available for PNR = 516 – 90rsv – 15taxi – 15%vbr = 358 Lt for flight

Subtract the climb & descent fuel Descent (approx) = (0.667 x 35nm) = 24lt358 – 20lt climb – 24lt descent = 314 lt for PNR277nm + 35nm = 312nm from departure aerodrome

destinationdeparture PNR

GS out =210kt

GS home =90kt

Wind +30kts tail

from TopC

20lt

35nm

277nm

4. Demonstrating PNRPractical method – Enroute

Enroute made from a positive fix & similar to the climb/descent, subtract the outbound/inbound fuel.

Eg: Outbound/inbound TAS = 180kts, fuel flow 100lt/hr, total fuel 516lt, wind 20kts tailwind outboundPositive fix = 80nm from departureHow far from departure is the PNR?

Fuel available for PNR = 516 – 90rsv – 15taxi – 15%vbr = 358 Lt for flight

Subtract outbound & inbound fuel outbound (approx) = (0.5 x 80nm) = 40ltInbound (approx) = (0.588 x 80nm) = 47lt358 – 40 – 47 = 271lt for PNR from fix249nm + 80nm = 329nm from departure aerodrome

destinationdeparture PNR

GS out =200kt

GS home =170kt

Wind +20kts tail

from fix

40 lt

80nm

47 lt 249nm

4. Demonstrating PNRSummary of PNR

destinationdeparture PNR

Cruise out & back PNR for planning

destinationdeparture PNR

Cruise out return asymmetric (lower alt)

destinationdeparture PNR

TopCPlanned PNR out & return with climb/descent

TopD

destinationdeparture PNR

Outbound fuel

Inbound fuel

Inflight PNR out & return from positive fix

5. Summary Summary of PNR vs CP/ETP

• The distance to the PNR depends on the flight fuel available Changes to reserves, variable reserves, holding, airwork etc

• Distance to the CP/ETP is independent of flight fuel.• The only time fuel is to be considered is if the pilot wishes to know how much fuel

will be burnt passed the ETP• Once past the PNR the aircraft will not be able to return to the departure airport with full

reserves/fuel intact • If the aircraft returns to departure at the ETP he/she will have reserves & excess fuel

intact

Questions?