At what exact point in time should we be giving the 10 minutes to diversion call to ATC?

Question

I wanted to get some clear information if it’s available as to which exact point should the 10 mins to diversion call be given to ATC with respect to our FOB. The way I have been doing it currently on the A320 is by looking at the FUEL PRED page and when that shows a time value equivalent to 10 mins I give the call to ATC. But this is not a very reliable way to do it while in a HOLD. As the FMGC only updates the extra fuel and time value after crossing the waypoint/PPOS/pseudo waypoint at which the hold has been inserted.

This 10 mins to diversion call is mainly given while flying in India to let ATC know that we only have 10 mins worth of extra fuel left for holding beyond which a diversion will have to be initiated to our filed destination alternate.

Is there any precise way to calculate when we will exactly be at 10 mins?

Answer 1

(I just came up with this, so it may not be the official solution - but it should be fairly simple this way)

You first need to know the fuel you need for the diversion with all safety requirements included. This is computed like normal using the MCDU, EFB, etc.. I'll call this your "bingo" fuel. You just need to add the fuel required a 10 minute period for your current flight situation. Once your FOB on the upper ECAM reaches that final result, call ATC.

The easiest way to compute the fuel required for the next 10 minutes is with the fuel flow indication.

On the engine display you have the fuel flow indication, which should be nearly constant during a hold at constant speed and constant altitude.

• Add all fuel flow values together
• Round up to the nearest 20 kg/hr or so to be safe
• Then divide the total fuel flow by 6 (10 min = 1/6 of an hour) to give you fuel required for a 10 minute hold at the current conditions.

Example:

Let's say each of the two engines shows a fuel flow of 1000 kg/hr. Add together to get 2000. Then divide 2000 kg/hr by 6 to get roughly 340 kg fuel consumption for the next 10 minutes. Add this to your bingo fuel.

( 1000 + 1000 ) / 6 = 333 -> 340 ... (+ bingo fuel)

Quicker Alternative:

You could also take the higher of the two engine fuel flow values and divide by 3. Then round up:

1000 kg/hr divided by 3 = 333 kg -> 340 ... (+ bingo fuel)

Note: This works the same if you have fuel flow in pound per hour. The result will be in pounds of fuel required for 10 minutes.

Answer 2

Yes what you ask is definitely possible.

You need to do the following:

Flight Plan: Ensure the flight plan accurately reflects what you expect to do. So you should have a STAR and an approach to the runway in use. Presumably the hold will be on the arrival in use. If it’s not then enter the hold, followed by a discontinuity in the flight plan (enter any waypoint and then delete it) and ensure the routing after the discontinuity reflects what you expect to do. The FPLN should look like this:

HOLD

ILS 22

Alternate: at the bottom of the FPLN will be your alternate. Make sure it has the routing you expect as per your company-issued flight plan, including the arrival and approach to landing runway. Input the average wind component (also shown on the flight plan). Now select your DESTINATION and input a SID that will join up with your intended routing to the ALTERNATE. Remove any discontinuity in the flight plan. Use the PLAN view on the ND which should show what you expect to be an accurate routing from your destination to the alternate.

FUEL PRED page: the fuel for your alternate should now be accurate as you have input your expected route to your alternate together with the wind component. Also ensure the final reserve is entered as per your flight plan.

The time remaining will now show how long is left until you have ALTN + FINAL RES fuel remaining. You’ll be able to work out how long is left until you have 10 mins to diversion time.

Note: the above is only accurate if you input the routing you can reasonably expect to follow.

Bonus tip: for example, if your alternate is north of your destination it may make sense to request a hold to the north of your destination - you’ll be closer to your alternate if you do decide to divert.

Answer 3

I think it would be mostly your discretion on when you decide to divert. I don't really get your question, but I think what you mean is at what amount of fuel should you request a diversion and notify ATC. For this, it depends on the plane model, weather condition, and much more.

For this example, let's say we're in a 737 approaching Toronto Pearson. We've just previously had two go arounds, and we'realmost on emergency fuel, with 40 minutes of fuel left. If the weather is clear, and you feel comfortable with the approach, you should probably notify ATC, but there is no reason to divert. On the other hand, if the weather is not clear and/or you don't feel comfortable with the approach, you can divert to another airport that you feel comfortable with or the weather is better there. , and if the weather's good, you can simply just declare an emergency and change runways.

If you divert, you should probably go to an airport that 1. is close to your current location (15 minutes away at tops) 2. has good weather and an easy approach, 3. meets your aircraft requirements. If you were at YYZ, the airports that you could divert to include Hamilton, Downsview, and if you've got enough fuel, you can try crossing the lake for Buffalo or Niagra. And if all 3 of these options are not able, you'll have to perform a ditching in the lake.

And as for the ten minute diversion call, it simply means when you have 10 minutes of fuel remaining + the emergency fuel. If you're at this stage, you MUST declare an emergency and divert if the weather or approach is not showing mercy.

I know this was a very complicated and long answer, but since we're all in quarantine, I figured we could all use up some more time. Hope I successfully answered your question, and I'm sorry no one else did.