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NZ FMS Holding Fuel Burn Predictions

NZ FMS Holding Fuel Burn Predictions

NZ FMS Holding Fuel Burn Predictions

Inside the FMS

“Ski Express 1234, I have holding instructions for you. Advise when ready to copy.” After fumbling for a pen and copying the holding clearance, you program the hold into the FMS. The FMS predicted fuel upon arrival at your destination just decreased. Have you ever wondered why it decreased by that particular amount? Or upon what assumptions the decreased arrival fuel is predicated?

When a holding pattern is defined and inserted into the active flight plan, the Honeywell NZ FMS assumes that once the holding fix is reached, the airplane will complete one circuit in the hold, and then continue to the destination via the remainder of the active flight plan.

For this example, ATC assigned holding at the FORPE intersection. Figure 1 shows 3,000 lbs of arrival fuel at KDEN prior to inserting the hold at FORPE.

Figure 1 – Predicted Arrival Fuel Prior to Inserting Hold

After the hold at FORPE is activated into the active flight plan, the arrival fuel at KDEN is reduced from 3,000 lbs to 2,900 lbs to account for a single circuit in the hold (Figure 2).

Figure 2 – Predicted Arrival Fuel After Inserting Hold

However, if the hold is not exited after completion of the first circuit, the FMS updates the arrival fuel to account for an additional circuit in the hold. Figure 3 shows a further reduction of the arrival fuel at KDEN once FORPE is crossed at the completion of the first circuit and beginning the second circuit of the hold.

Figure 3 – Predicted Arrival Fuel Upon Commencing Second Circuit in Hold

Iterative updating of the arrival fuel continues with each additional circuit in the hold. In other words, the FMS fuel predictions take it one circuit in the hold at a time. This is important to know and understand when using the destination fuel predictions in a divert decision during extended holding.

Program Pilot Ryan Milmoe supports Embraer and Dassault EASy for Honeywell Flight Technical Services. He can be reached via email at Ryan.Milmoe@Honeywell.com