Aircraft performing below book numbers

Antonio wrote:

What does it change in practice other than making a mayday fuel situation once you reach your final reserve?

I’d say that for both VFR and IFR it means that you can’t use the reserve as “holding” fuel.

I teach navigation and flight planning at our club school. Previously all fuel calculations have been trip fuel computed exactly as per the POH (taking forecast wind into account of course) plus the reserve fuel as that is what the CAA expects to see on the tests.

Now we have to start introducing contingency fuel. Of course I have mentioned that in practice you should add contingency fuel anyway but now the regs require it. The interesting question is how the CAA is going to test that. Are they going to state in the exams that you should e.g. use 10% contingency fuel for the calculations? I’ve better ask my CAA…

Mooney_Driver wrote:

What the final reserve has changed now is that while before it was possible to fly down to 45’ of fuel left in tanks to your destination and use the 45 mins to then go elsewhere, with the new regulation that fuel is off limits.

Not quite.

Old version: You had to take into account contingencies (weather, ATC routing/delays, any other condition that might cause delay or increase in fuel consumption – see old NCO.OP.125 clause (b)). So a diversion to an alternate on final reserve should be extremely rare.

New version: You have to consider “the likelihood of unexpected circumstances that the final reserve fuel/energy may no longer be protected” (NCO.OP.125 (b) (2)

So now and previously, in day VFR you need to judge whether you anticipate needing an alternate, if you do than you need to have that as contingency; if you think a diversion is highly unlikely you don’t need to carry diversion fuel. You also need a contingency for, say, adverse wind, or having to orbit at the destination .

So in practice the new rules are not more restrictive.

In fact, they give MORE leeway – They now allow you to consider the risk you pose by running out of fuel (NCO.OP.125 (b) (1) – so in principle we can now say “hey, my alternate route leads over wide open fields so I don’t pose much risk”. Or (which was probably the regulatory intent) “I am flying an electric Quadcopter which can fly for only 30 minutes on a nice day, but it has vertical autoland so running out of energy is ok”, and hence lower the final reserve. The precise rules (which are pretty much the old rules) have been relegated to an AMC, and you can come up with an alternate means of compliance, as long as you make an appropriate risk assessment.

Isn’t this mostly of relevance for electric planes? I mean 10 minutes of reserve, 30 minutes of reserve. There is no way you are able to determine in flight if you have 10 or 30 min left unless:

• You are flying an electric aircraft
• You run the main tank(s) dry and have a separate tank with 10 or 30 min left (which some planes have, like the Savannah, also the Safir by the way. Not minutes but an exactly known quantity)

The only other way to know this with some degree of accuracy (by no means enough accuracy for those calculations, but still) is to:

• know exactly how much fuel you have on take off.
• Have a totalizer with super high accuracy

Margins are there to account for impossible calculations and planning. They aren’t there to calculate them exactly in flight when this is impossible.

@Cobalt wrote:

Not quite.

You were quoting Mooney_driver, not me.

Cobalt wrote:

So in practice the new rules are not more restrictive.

So do I see the following correctly or not?

- Under the new rule, the final reserve is protected fuel which means it MUST be on board on arrival, wherever that arrival may be. If it’s not, we are talking of a low fuel incident which requires a compulsory report to the CAA and will prompt an inquiry and possible action. (That is what has been in use for CAT for as long as I can think back).

- Under the old rule, you had to have 45 mins VFR reserve on arrival but it was fine to go into that if you needed to. In many cases it was used to cover contingency fuel. E.g. if you arrived at your destination with say 1 hr of fuel and had to wait for 20 mins, it was ok to take that decision and break into the 45 mins.

- Under the new rule, if you arrive with 1 hr at your destination, you MUST be on the ground before you reach final reserve otherwise it’s a Pan Pan or even Mayday and will trigger an investigation. Quite possibly, the intent was to force this as people will shut up about their predicament too often and run out of fuel?

Alternate fuel was always on top of that. No change there. I personally also used a route reserve and contingency fuel, but it was not obligatory to do so.

If my understanding of the new rule is correct, this de facto means that the route reserve, for planning purposes, becomes “unusable fuel”. If you are ramp checked on arrival and carry less fuel than final reserve it would be a violation?

While my own planning won’t change much as I always have treated those 45 mins as a final reserve, it still has impact in as so far that you need to basically add additional reserves in order not to break into those 45 mins of fuel.

Or do I understand this wrong?

These are planning minima. While the AMC says that if you go below you should consider this an emergency, but you din’t have to, nor is it a MOR event. In the end it is still a judgement call – a mayday with 29 minutes of fuel on downwind to land in an empty circuit is silly. If I then ended up going around in a busy circuit because people dawdle on the runway, on the second approach with two ahead I would use the M-word.

My point is that you always had to have contingency fuel on top of the final reserve. People who did regularly use the final reserve as contingency fuel for other things were doing it “wrong” under both rules.

Cobalt wrote:

While the AMC says that if you go below you should consider this an emergency, but you don’t have to, nor is it a MOR event.

Yes, it does say “should” and not “shall” and for part-NCO you can make your own AltMOC, but still…

Mooney_Driver wrote:

If you are ramp checked on arrival and carry less fuel than final reserve it would be a violation?

Is checking fuel level something ramp checkers are entitled to do? Checking documents and flight preparation for sure but for anything more I would have told them to take a hike.

Clipperstorch wrote:

Is checking fuel level something ramp checkers are entitled to do?

I’ve seen it done on airliners after they reported low fuel. And I’d be very sure they’d do that on a GA plane if you follow the rules and declare pan pan or mayday.