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# Critical Pts & Pts of No Return

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Critical Pts & Pts of No Return
ATC Chapter 5

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

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

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.

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

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 )

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

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

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

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

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

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

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

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

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

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

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

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

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