Hi, I am preparing for my CPL performance exam and I’m working through the performance study guide (a slightly older version Dec 2021 but checking against errata).

Part 135 chapter 7 states contingency fuel should be 10% of trip fuel, but a lot of the examples on the Performance book apply the 10% contingency to ALL of the remaining fuel after reserves and taxi have been considered. Unless I am mistaken this applies 10% contingency to the trip fuel AND any extra fuel one may be carrying rather than just to the trip fuel.

Tried to find a clear answer on the forum to this one but could not. Would appreciate any guidance as using the wrong method in the exam will have a knock on effect on the correctness of many answers across the exam. Thanks

Hi Stratus. This calculation depends on what you are trying to calculate. If calculating the minimum fuel required, then the contingency fuel is calculated on your known trip fuel. If working in reverse, how much trip fuel would be available or safe endurance with a given fuel in tanks figure? In this case, the fuel remaining after removing final reserve fuel, startup and taxi, and any holding or alternate fuel is trip fuel plus contingency.
Cheers W

Thanks for the quick reply Wayne. I was thinking of a scenario where you were carrying additional fuel (not required by the trip or reserves) in that case if you worked back from total fuel amount removing final reserve fuel, startup and taxi, and any holding or alternate fuel and then divided that number by 1.1 you would be applying the contingency factor to both the trip fuel and any additional fuel being carried

This is a good example of what I was wrestling with. The question is from the Performance Final Test question 8. You are given the transit fuel, so could work out the 10% contingency just on the transit fuel and leave more for the search...or you could take the 10% off the total fuel less reserves and then subtract the transit fuel to get the search fuel available. Each approach will give a different answer. I have seen different approaches used for these sort of questions (across Bob Tait and other online CPL practice exams). Any clarity welcome. Thanks

Hi Stratus,

The answer lies in Part 135 MOS, Chapter 7 and definitions. While it does not talk about search fuel directly, there is a definition of Trip Fuel, upon which contingency fuel is calculated. Para 7.02 defines trip fuel as the amount of fuel required to enable an aeroplane to fly from
any point along the route until landing at a destination aerodrome, plus a few other points. So while in the search area, you are not actually flying along the route to your destination, so no contingency fuel is needed for your search area fuel.
Cheers W

The Answer in the latest text book is (b) 262 minutes.

Thanks Wayne for the quick response. The definition of what is and is not contingency fuel above makes practical sense, but the math to get to the 262 minute answer in the book appears to take the 10% contingency off the total fuel less final reserve, rather than just 10% on the trip fuel

130 Gal - 15 Gal final reserve / 1.1 =104.5 Gal - transit fuel 30 Gal = 74.5 Gal @ 17.2 Gal/hr = 259.9 minutes
whereas if 10% contingency is ONLY applied to the trip fuel
130 Gal - 15 Gal final reserve - (transit fuel 30 Gal * 1.1) = 82 Gal @ 17.2 Gal/hr = 286 minutes

...quite a big difference and enough to get the answer wrong

Hi Stratus. My mistake, but search area fuel must be included with trip fuel and contingency applied to both. Your answer differs slightly, as the text book has rounded the Trip Fuel up to a whole decimal point. On the CASA exam website, they recommend keeping the decimal point until the final answer.
Cheers W

I guess it's a matter of definition. Is a search for a missing boat classified as air transport? There is nothing to stop an operator from adopting a fuel policy that requires contingency fuel on all flights undertaken by the company. The question said "your operator requires you to allow contingency fuel on all flights". So just do what the question says.

Thanks Bob and Wayne