Fuel Planning to Puerto Princesa with a Marginal Alternate
You are planning a Piper PA-34 Seneca V IFR from Manila to Puerto Princesa, a 2+00 leg. The aircraft has 120 gal usable and you plan to depart with 100 gal. Cruise burn is 24 gph at 9,000 ft, and taxi fuel is 2 gal. Puerto Princesa is forecast 700 ft overcast with 2,500 m visibility and has an RNAV approach with LNAV minima of 400 ft. Your alternate, San Jose (Mindoro), is 0+45 away, forecast 1,500 ft broken with 6 km, VOR MDA 800 ft. You plan a 45-minute reserve and a 15-minute contingency, plus 10 minutes for an approach and missed approach. Forecast winds give a 15 kt headwind, which adds about 12 minutes to the leg.
1. Compute the fuel required and decide whether 100 gal is sufficient.
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Trip 2:00 at 24 gph = 48 gal. Headwind +12 min = 0.2 h × 24 = 4.8 gal, so use about 53 gal for the leg. Alternate 0:45 = 18 gal. Reserve 0:45 = 18 gal. Contingency 0:15 = 6 gal. Approach/missed 0:10 = 4 gal. Taxi = 2 gal.
Total = 101 gal, which already exceeds the 100 gal on board-before any hold. Even without the headwind, the total is 96 gal, leaving only a 4 gal (10 min) margin, which is not prudent.
You should either reduce payload and take more fuel (the aircraft can carry 120 gal usable), add a fuel stop, or postpone. The legal minimum is not the same as a safe margin; with a destination forecast at 700/2,500 you should expect at least one approach and a possible diversion.
2. Is San Jose a legal alternate under the forecast conditions?
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Because Puerto Princesa is forecast below 2,000 ft ceiling and 5,500 m visibility, an alternate is required under Philippine IFR planning rules.
San Jose at 1,500 ft broken and 6 km is above the usual non-precision alternate minima (ceiling at or above MDA + 400 ft and visibility at least 3,200 m, or the published alternate minima). With an MDA of 800 ft, the ceiling requirement is about 1,200 ft; 1,500 ft satisfies it.
So the alternate is legal, but check the published alternate minima and the forecast validity period. If San Jose were forecast 1,000/3,000, it would not be a legal alternate, and you would need a second alternate or enough fuel to hold at Puerto Princesa until conditions improve.
3. In flight, ATC gives you a 20-minute hold at Puerto Princesa. What is your fuel state, and what do you do?
Read the worked answer
Fuel remaining at the hold = 100 − 2 taxi − 53 trip = 45 gal. A 20-minute hold at 24 gph burns 8 gal, leaving 37 gal.
The fuel needed to reach San Jose is 18 gal plus 18 gal reserve = 36 gal, so you would land with only 1 gal above reserve-effectively no margin. Declare minimum fuel before the hold begins, or divert immediately.
If the hold is for weather at Puerto Princesa, set a limit of about 5 minutes; beyond that, leave for San Jose. Also account for the missed approach at Puerto Princesa (4 gal). Do not accept a holding clearance that leaves you below reserve; tell ATC your fuel state and request a diversion.