Hi All,

I just missed out on passing the Performance exam (69%). I was scoring quite well in the practice exams but found the actual exam more challenging than expected. There are a few questions I was unsure how to answer and hopefully someone on the forum might be able to assist:

I had a PNR question where no Fuel On Board figures were provided which caught me off guard given I've only seen questions with FOB at Start or Takeoff. Instead the Trip Time/Fuel was provided. If FOB figures are not given, is it as straightforward as converting trip fuel to trip time which would be the Safe Endurance? I ignored other fuel requirements such as holding and alternate.

I had four questions that involved takeoff/landing charts. When I was trying to figure out maximum takeoff weight or minimum landing distance, I would for example consider a 15 kt tailwind with an upslope for landing or downslope for takeoff however the charts do not allow for tailwinds greater than 5 kts. Does that mean a tailwind greater than 5 kts should not even be considered and I should only entertain a runway heading with a headwind?

Hopefully my questions are not too vague.

Thanks in advance!

Ranj

I just missed out on passing the Performance exam (69%).

That's a bad hand to be dealt. Never mind, the odd failure along the way to a licence is character building.

I had a PNR question where no Fuel On Board figures were provided

One of the problems with applying canned solution techniques is that it makes for confusion when the problem is a bit different to what you have practised. Suggest you consider using a standard fuel planning calculation for all fuel problems. Fill in what you know (or are given) and then figure out what you don't know to complete the table and then select which bits are of use for the problem. Works a treat every time.

I would for example consider a 15 kt tailwind

Generally data will be done for 10 kt tailwind. Sometimes the data for an aircraft will be extended, although generally not beyond 20 kts. Regardless, if the published POH data only goes to 5 kt, then that is your LIMIT and you MUST NOT extrapolate. So, if the maximum tailwind on the chart is 5 kt, then you may not plan on using the runway.

Likewise you cannot extrapolate beyond any of the end data points for other parameters such as slope.

Thanks John. Appreciate the feedback.

With regards to Safe Endurance on a PNR question, if I have trip fuel or trip time already provided should I run with that value as my Safe Endurance (if no Fuel on Board quantities are provided)? I believe this assumption to be correct but wondering if I'm missing anything else if for example an alternate aerodrome is provided.

Point taken on the takeoff/landing charts. Basically if a tailwind or headwin is more than what is provided in the chart then do not plan for that paricualr runway heading.

.. if I have trip fuel or trip time already provided should I run with that value as my Safe Endurance ...

For many cases, probably yes. However, we probably need a bit more of the story to proceed specifically. While the AC gives some basics, one needs to keep one's wits about oneself - sometimes it is prudent to be more conservative than the AC minimums. If you like to run up a specific scenario, perhaps we could speak to that story ?

Basically if a tailwind or headwind is more than what is provided in the chart then do not plan for that particular runway heading.

If you have a headwind, you can operate (consistent with any handling considerations for the Type) with a headwind greater than that provided in the POH charts but you can't take any credit for the part of the headwind which is greater than what is published in the POH chart. For example, if your chart has a maximum 20 kt headwind (which is pretty typical), but the actual headwind is, say, 30 kt, then you can only take credit for 20 kt in figuring out your maximum weight.

If the question gave you trip fuel only and said nothing about the fuel policy of the aircraft you are flying regarding reserves or allowances I would consider it to be an invalid question. Even if you tried to add the final reserve fuel and taxi allowance (absolutely necessary), where are you supposed to find that information from the text of the question.

The ONLY fuel figures you need for a PNR calculation are the total fuel on board and the reserves and allowances. The tirp fuel has nothing to do with a PNR unless the questions specifies minimum fuel. Even then you would need to be told the ETI and fuel flow.

I find it hard to believe that CASA would present the question as you have described it. Are you sure you haven't missed something in your recollection of the wording?

Hi Bob,

Just to clarify the question did provide startup fuel, alternate fuel, final reserve, trip fuel (and maybe holding). I cannot recall whether it was a private or air transport flight but I understand the Part 91 and Part 135 fuel requirements for contingency and final reserve.

For a PNR question I was expecting to see Fuel on Board at start or takeoff instead of the individual fuel requirements mentioned above. Thus for the Safe Endurance I just took the trip fuel plus any contingency, converted to time based on fuel flow data to get trip time as my safe endurance. Does that sound correct?

Just one more question I've been trying to figure out all over the message boards and internet. What are the conditions under which an aeroplane will achieve maximum range and endurance? This is out of Part 61 1.9.5, 3.1.1 (d). Thanks!

That still seems odd to me. All you need is the actual fuel on board at start up. If they give you trip fuel, final reserve fuel, holding fuel and alternate fuel, they would still have to specify that you are carrying minimum fuel for the flight. Did you have any margin fuel?

A PNR has nothing to do with the flight you are planning. A PNR calculation begins when you dip the tanks before start-up. That's the figure you start with. Then take out reserves and holding, if it applies to the departure aerodrome. (a PNR considers the departure aerodrome to be the destination since you are planning on return to the departure aerodrome).

As far as maximum range is concerned, you fly at best ground nautical miles per gallon (ground speed ÷ fuel flow). Aerodynamically, that's the angle of attack that produces the best lift/drag ratio. It would depend on the answer choices given.

Endurance is an easy one. Fly at the minimum fuel flow (minimum power). In practice, that may be so slow as to produce sluggish control response. In that case, your flight manual will specify an appropriate power setting.

Thanks Bob. As far as I can recall no margin fuel was provided but perhaps the format of the question threw me off and I missed some key details.

The language in Part 61 1.9.5, 3.1.1 (d) seems vague to me as it appears to ask for conditions that achieve both max range and endurance whereas I thought they are mutually exclusive. My understanding was that minimum power (endurance) is opposite to best ground nm per gallon (range). Nonethelss your feedback makes perfect sense. Thanks.

You are not the only one who finds the CASA regulatory documents difficult (almost impossible) to read. They were written by lawyers for lawyers before a magistrate. They are not interested in communicating information to aviators. Unfortunately, I don't think it will get any better.