1. Critical Pts & Pts of No Return
ATC Chapter 5

2. Aim
To identify operational considerations for flight planning, and demonstrate the use of calculating Critical Points & Points of No-Return

3. Objectives Define the Critical Point
Demonstrate method of Critical Point
Define the Point of No-Return
Demonstrate method of PNR
Summary of the above

4. 1. Define Critical Point What 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.
45min
45min
Departure
Critical Point
Destination
In nil wind where would the critical point be?
In the middle!
If there is wind, this will move the critical point into wind.

5. 1. Define Critical Point What is a Critical Point?
The equation for the critical point is:
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑜 𝐶𝑃= 𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 ×𝐺𝑟𝑜𝑢𝑛𝑑 𝑆𝑝𝑒𝑒𝑑 𝐻𝑂𝑀𝐸 𝐺𝑆 𝑂𝑈𝑇+𝐺𝑆 𝐻𝑂𝑀𝐸
Remember, ground speed will be affected with wind.
Calculations for accurate ground speeds out & back must be calculated.
Critical Point
GS Home
GS OUT
Departure
Total Distance
Destination

6. 𝑫 𝑨 = (𝑫 𝑻𝒐𝒕𝒂𝒍 ×𝑺 𝒉𝒐𝒎𝒆 ) (𝑺 𝒐𝒖𝒕 + 𝑺 𝒉𝒐𝒎𝒆 )
1. Define Critical Point
How is the CP derived?
The CP is the point where;
𝑇 𝐻𝑂𝑀𝐸 = 𝑇 𝑂𝑈𝑇
𝐷 𝐴 𝑆 ℎ𝑜𝑚𝑒 = 𝐷 𝐵 𝑆 𝑜𝑢𝑡 , where DB = Dtotal – DA
𝐷 𝐴 𝑆 ℎ𝑜𝑚𝑒 = 𝐷 𝑇𝑜𝑡𝑎𝑙 − 𝐷 𝐴 𝑆 𝑜𝑢𝑡
multiply both sides by Shome & Sout
𝐷 𝐴 𝑆 ℎ𝑜𝑚𝑒 𝑆 ℎ𝑜𝑚𝑒 .𝑆 𝑜𝑢𝑡 = 𝐷 𝑇𝑜𝑡𝑎𝑙 − 𝐷 𝐴 𝑆 𝑜𝑢𝑡 𝑆 ℎ𝑜𝑚𝑒 .𝑆 𝑜𝑢𝑡
𝐷 𝐴 .𝑆 𝑜𝑢𝑡 = 𝐷 𝑇𝑜𝑡𝑎𝑙 .𝑆 ℎ𝑜𝑚𝑒 − 𝐷 𝐴 .𝑆 ℎ𝑜𝑚𝑒
𝐷 𝐴 .𝑆 𝑜𝑢𝑡 + 𝐷 𝐴 .𝑆 ℎ𝑜𝑚𝑒 = 𝐷 𝑇𝑜𝑡𝑎𝑙 .𝑆 ℎ𝑜𝑚𝑒
𝐷 𝐴 (𝑆 𝑜𝑢𝑡 + 𝑆 ℎ𝑜𝑚𝑒 )= 𝐷 𝑇𝑜𝑡𝑎𝑙 .𝑆 ℎ𝑜𝑚𝑒
𝑫 𝑨 = (𝑫 𝑻𝒐𝒕𝒂𝒍 ×𝑺 𝒉𝒐𝒎𝒆 ) (𝑺 𝒐𝒖𝒕 + 𝑺 𝒉𝒐𝒎𝒆 )

7. 2. Use of the CP Method Flying from YPPF to YMIA
Total distance is 210nm
20kt tail wind outbound from YPPF to YMIA
TAS = 120kts
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑜 𝐶𝑃= 𝑇𝑜𝑡𝑎𝑙 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 ×𝐺𝑟𝑜𝑢𝑛𝑑 𝑆𝑝𝑒𝑒𝑑 𝐻𝑂𝑀𝐸 𝐺𝑆 𝑂𝑈𝑇+𝐺𝑆 𝐻𝑂𝑀𝐸
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑜 𝐶𝑃= 210× =87.5 𝑛𝑚
Critical Point = 87.5nm from YPPF
GS Home = 100 kt
GS out = 140 kt
YPPF
Total Distance = 210
YMIA

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

9. 3. Define the PNR What 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
Beyond this point, if the aircraft turns back it will not be able to land with reserves infact
departure
PNR
destination

10. 3. Define the PNR Considerations?
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
departure CP
PNR
destination

11. 𝑻 𝒐𝒖𝒕 𝒕𝒐 𝑷𝑵𝑹 = 𝑺 𝒉𝒐𝒎𝒆 𝑬𝒏𝒅 𝑺 𝒐𝒖𝒕 + 𝑺 𝒉𝒐𝒎𝒆
3. Define the PNR
How is the PNR derived?
The PNR is the point where;
𝐷 𝑜𝑢𝑡 𝑡𝑜 𝑃𝑁𝑅 = 𝐷 ℎ𝑜𝑚𝑒 𝑡𝑜 𝑃𝑁𝑅
𝑆 𝑜𝑢𝑡 × 𝑇 𝑜𝑢𝑡 = 𝑆 ℎ𝑜𝑚𝑒 × 𝑇 ℎ𝑜𝑚𝑒
where THome = Endurance Available – TOUT
𝑆 𝑜𝑢𝑡 × 𝑇 𝑜𝑢𝑡 = 𝑆 ℎ𝑜𝑚𝑒 𝐸𝑛𝑑 − 𝑇 𝑜𝑢𝑡
𝑆 𝑜𝑢𝑡 𝑇 𝑜𝑢𝑡 = 𝑆 ℎ𝑜𝑚𝑒 𝐸𝑛𝑑− 𝑆 ℎ𝑜𝑚𝑒 𝑇 𝑜𝑢𝑡
𝑆 𝑜𝑢𝑡 𝑇 𝑜𝑢𝑡 + 𝑆 ℎ𝑜𝑚𝑒 𝑇 𝑜𝑢𝑡 = 𝑆 ℎ𝑜𝑚𝑒 𝐸𝑛𝑑
𝑇 𝑜𝑢𝑡 𝑆 𝑜𝑢𝑡 + 𝑆 ℎ𝑜𝑚𝑒 = 𝑆 ℎ𝑜𝑚𝑒 𝐸𝑛𝑑
𝑻 𝒐𝒖𝒕 𝒕𝒐 𝑷𝑵𝑹 = 𝑺 𝒉𝒐𝒎𝒆 𝑬𝒏𝒅 𝑺 𝒐𝒖𝒕 + 𝑺 𝒉𝒐𝒎𝒆

12. 𝑻 𝒐𝒖𝒕 𝒕𝒐 𝑷𝑵𝑹 = 𝑺 𝒉𝒐𝒎𝒆 𝑬𝒏𝒅 𝑺 𝒐𝒖𝒕 + 𝑺 𝒉𝒐𝒎𝒆
4. Demonstrating PNR
Planning method
𝑻 𝒐𝒖𝒕 𝒕𝒐 𝑷𝑵𝑹 = 𝑺 𝒉𝒐𝒎𝒆 𝑬𝒏𝒅 𝑺 𝒐𝒖𝒕 + 𝑺 𝒉𝒐𝒎𝒆
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 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?
𝑻 𝒐𝒖𝒕 𝒕𝒐 𝑷𝑵𝑹 = 𝟏𝟔𝟎×𝟒.𝟐 𝟐𝟎𝟎+𝟏𝟔𝟎 =𝟏.𝟖𝟕 𝒉𝒐𝒖𝒓𝒔 𝒕𝒐 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
GS out =200kt
Wind +20kts tail
departure
GS home =160kt
PNR
destination

13. 4. Demonstrating PNR Practical 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
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
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 𝑜𝑢𝑡 = 100 𝑙𝑡/ℎ𝑟 200𝑘𝑡𝑠 =0.5 𝑙𝑡/𝑔𝑛𝑚
Therefore, for every ground nautical mile flown, the aircraft burns 0.5 litres outbound
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 ℎ𝑜𝑚𝑒 = 100 𝑙𝑡/ℎ𝑟 160𝑘𝑡𝑠 =0.625 𝑙𝑡/𝑔𝑛𝑚
𝑫𝒊𝒔𝒕 𝒕𝒐 𝑷𝑵𝑹 𝒏𝒎 = 𝑭𝒖𝒆𝒍 𝑨𝒗𝒂𝒊𝒍𝒂𝒃𝒍𝒆 (𝒍𝒕) 𝑻𝒐𝒕𝒂𝒍 𝑩𝒖𝒓𝒏 𝒓𝒂𝒕𝒆𝒔 𝑮𝑺 𝒐𝒖𝒕 + 𝑮𝑺 𝒉𝒐𝒎𝒆 𝒍𝒕/𝒈𝒏𝒎
= =302𝑛𝑚

14. 4. Demonstrating PNR Practical method – Engine failure
Eg: Outbound TAS = 180kts, fuel flow 100lt/hr, total fuel 500lt, wind 30kts headwind outbound
Engine 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
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 𝑜𝑢𝑡 = 100 𝑙𝑡/ℎ𝑟 150𝑘𝑡𝑠 =0.667 𝑙𝑡/𝑔𝑛𝑚
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 ℎ𝑜𝑚𝑒 = 60 𝑙𝑡/ℎ𝑟 150𝑘𝑡𝑠 =0.4 𝑙𝑡/𝑔𝑛𝑚
𝑫𝒊𝒔𝒕 𝒕𝒐 𝑷𝑵𝑹 𝒏𝒎 = 𝑭𝒖𝒆𝒍 𝑨𝒗𝒂𝒊𝒍𝒂𝒃𝒍𝒆 (𝒍𝒕) 𝑻𝒐𝒕𝒂𝒍 𝑩𝒖𝒓𝒏 𝒓𝒂𝒕𝒆𝒔 𝑮𝑺 𝒐𝒖𝒕 + 𝑮𝑺 𝒉𝒐𝒎𝒆 𝒍𝒕/𝒈𝒏𝒎 = =321𝑛𝑚 from departure
GS out =150kt
Wind  – 30kts head
departure
GS home =150kt
PNR
destination

15. 4. Demonstrating PNR Practical 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 outbound
Engine failure TAS = 120kts, fuel flow 60lt/hr
Climb fuel = 20lt & 35nm
How 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) = 24lt
358 – 20lt climb – 24lt descent = 314 lt for PNR
277nm + 35nm = 312nm from departure aerodrome
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 𝑜𝑢𝑡 = 100 𝑙𝑡/ℎ𝑟 210𝑘𝑡𝑠 =0.476 𝑙𝑡/𝑔𝑛𝑚
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 ℎ𝑜𝑚𝑒 = 60 𝑙𝑡/ℎ𝑟 90𝑘𝑡𝑠 =0.667 𝑙𝑡/𝑔𝑛𝑚
𝑫𝒊𝒔𝒕 𝒕𝒐 𝑷𝑵𝑹 𝒏𝒎 = 𝑭𝒖𝒆𝒍 𝑨𝒗𝒂𝒊𝒍𝒂𝒃𝒍𝒆 (𝒍𝒕) 𝑻𝒐𝒕𝒂𝒍 𝑩𝒖𝒓𝒏 𝒓𝒂𝒕𝒆𝒔 𝑮𝑺 𝒐𝒖𝒕 + 𝑮𝑺 𝒉𝒐𝒎𝒆 𝒍𝒕/𝒈𝒏𝒎 =
=277𝑛𝑚 from TopC
GS out =210kt
20lt
Wind  +30kts tail
GS home =90kt
departure
277nm
PNR
destination
35nm

16. 4. Demonstrating PNR Practical 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 outbound
Positive fix = 80nm from departure
How 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) = 40lt
Inbound (approx) = (0.588 x 80nm) = 47lt
358 – 40 – 47 = 271lt for PNR from fix
249nm + 80nm = 329nm from departure aerodrome
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 𝑜𝑢𝑡 = 100 𝑙𝑡/ℎ𝑟 200𝑘𝑡𝑠 =0. 5𝑙𝑡/𝑔𝑛𝑚
𝐹𝑢𝑒𝑙 𝐹𝑙𝑜𝑤 𝐺𝑆 ℎ𝑜𝑚𝑒 = 100 𝑙𝑡/ℎ𝑟 170𝑘𝑡𝑠 =0. 588𝑙𝑡/𝑔𝑛𝑚
𝑫𝒊𝒔𝒕 𝒕𝒐 𝑷𝑵𝑹 𝒏𝒎 = 𝑭𝒖𝒆𝒍 𝑨𝒗𝒂𝒊𝒍𝒂𝒃𝒍𝒆 (𝒍𝒕) 𝑻𝒐𝒕𝒂𝒍 𝑩𝒖𝒓𝒏 𝒓𝒂𝒕𝒆𝒔 𝑮𝑺 𝒐𝒖𝒕 + 𝑮𝑺 𝒉𝒐𝒎𝒆 𝒍𝒕/𝒈𝒏𝒎 =
=249𝑛𝑚 from fix
GS out =200kt
Wind  +20kts tail
40 lt
GS home =170kt
departure
47 lt
249nm
PNR
destination
80nm

17. 4. Demonstrating PNR Summary of PNR departure PNR destination
Cruise out & back PNR for planning
departure
PNR
destination
Cruise out return asymmetric (lower alt)
departure
PNR
destination
TopC
Planned PNR out & return with climb/descent
TopD
departure
PNR
destination
Outbound fuel
Inflight PNR out & return from positive fix
departure
Inbound fuel
PNR
destination

18. 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

19. Questions?