EDCT, a RAIM Outage, and an ILS Out of Service
Flight 207, KPHX-KSAN, is planned with a 2015Z departure, 15 minutes taxi, and 1:05 enroute. ATC has assigned an EDCT of 2130Z wheels-up. KSAN forecast: 900 OVC, 2 SM BR. The ILS Runway 27 is NOTAM'd out and the only remaining approach is RNAV (GPS) Runway 27 with LNAV minimums of 700-1. A GPS NOTAM states 'RAIM unavailable 2100Z-2300Z' for the terminal area. The filed alternate KPSP is 35 minutes away and has an ILS. Planned fuel is 250 lb taxi, 2,200 lb trip, 1,800 lb 45-minute reserve, 900 lb alternate, and 200 lb contingency, for 5,350 lb. Fuel on board is 5,600 lb. The station wants to board immediately to protect the slot.
1. Work backward from the EDCT. What time does the aircraft need to push, and what does that do to the plan?
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The EDCT is a wheels-up time, so the plan runs backward: 2130Z minus 15 minutes taxi means brake release no later than 2115Z at KPHX. ATC allows only a small window around the assigned time; being early is as much of a problem as being late, and if the flight cannot make it the dispatcher must coordinate a new EDCT rather than launch and hope.
This means the aircraft sits on the ground for roughly an hour beyond the 2015Z planned departure. Boarding now is fine, but the plan must account for ground burn: APU and engine idle for 60 minutes is on the order of 150-300 lb depending on the APU. That comes out of the 250 lb margin, not out of the reserve. The dispatcher should also confirm the crew's duty clock started at the right point and that a gate hold does not push the arrival past a curfew or the crew's limit.
2. Does the destination require an alternate, and how does the RAIM outage change the picture?
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The alternate is required on two independent grounds.
First, 121.619: KSAN at 900 OVC and 2 SM is below 2,000-3 within the ETA window, so an alternate is mandatory regardless of equipment.
Second, and more serious: with the ILS out and RAIM unavailable from 2100Z to 2300Z, the destination has no usable instrument approach during the planned arrival. An LNAV approach that depends on GPS cannot be flown in that window. That does not make the flight illegal to dispatch, but it means the only realistic outcomes are holding until 2300Z or diverting to KPSP.
KPSP with an ILS satisfies 121.625 (600-2 for a precision approach) - but verify the alternate's forecast at the time the flight would actually arrive there, and verify the alternate does not itself depend on GPS. The dispatcher should also consider a departure delay of roughly 90 minutes so the arrival falls after the RAIM outage ends; that converts a probable divert into a normal arrival.
3. Assess the fuel plan and decide whether to release as loaded.
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Minimum fuel: 250 taxi + 2,200 trip + 900 alternate + 1,800 reserve = 5,150 lb. With the 200 lb contingency the plan is 5,350 lb against 5,600 lb on board - a 250 lb margin, which is about 7-8 minutes of holding at typical hold burn.
That margin is not adequate for this flight. The arrival window has a RAIM outage that may force holding to 2300Z, on top of an hour of anticipated ground burn from the EDCT. Twenty to thirty minutes of holding fuel (roughly 700-1,000 lb) is the right planning allowance, and it should come on top of the alternate and reserve, not out of them.
Decision: do not release at 5,600 lb. Either add fuel, or shift the ETD so the arrival is after 2300Z and the RAIM-driven hold disappears. If the flight goes as loaded, the dispatcher should expect a divert to KPSP and should be prepared to issue an amended release with the new fuel state.