Fuel Management with In-flight Icing and ATC Reroute
You are pilot-in-command of a twin-engine turboprop (MTOW 5,700 kg) on a scheduled IFR flight from Brunei International (WBSB) to Miri (WBGR). Planned trip fuel is 420 kg, taxi 30 kg, contingency 5% of trip (21 kg), alternate fuel to Limbang (WBGG) is 180 kg, final reserve 45 minutes at 600 kg/h (450 kg). Take-off mass is 5,200 kg; fuel on board at startup is 1,150 kg. About 40 NM after departure, ATC advises that weather at Miri has deteriorated to visibility 1,200 m in heavy rain and the ILS is unserviceable; you may expect a VOR/DME approach. You also encounter moderate icing at FL120 and request a lower level; ATC clears you to FL080, which adds 15 minutes to the remaining route. Your anti-ice system increases fuel flow by 8%. You must decide whether to continue to Miri, divert to Limbang, or return to Brunei.
1. Calculate the minimum fuel required to continue to Miri under the new conditions (including the extra 15 minutes and anti-ice penalty) and compare it with the fuel remaining. Show your reasoning and state whether a diversion is required.
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First, recompute the fuel needed from the present position. Original trip fuel from take-off to Miri was 420 kg. The extra 15 minutes at the normal cruise flow (assume cruise flow = 600 kg/h, since final reserve is 45 min at 600 kg/h) adds 150 kg. The anti-ice penalty applies to the remaining trip fuel: the remaining trip fuel is roughly the original trip fuel minus fuel already used. Fuel used from startup to the present position is not given directly, but we can estimate: taxi 30 kg plus about 40 NM at cruise speed. Without a cruise speed, we cannot compute exact fuel used. However, the question asks for the minimum fuel required to continue from the present position, not from take-off. A practical method is to use the planned fuel figures and adjust: the planned fuel at this point would have been trip fuel remaining plus contingency plus alternate plus final reserve. Because the scenario does not provide fuel used so far, we must make a reasonable assumption or state that the calculation requires the actual fuel remaining. The key operational point is that the added 15 minutes (150 kg) plus 8% anti-ice penalty on the remaining trip fuel (say, if 300 kg remains, penalty is 24 kg) increases required fuel by about 174 kg. The alternate fuel to Limbang (180 kg) and final reserve (450 kg) remain unchanged. If fuel remaining is 1,150 kg minus (30 kg taxi + fuel used), and fuel used is unknown, we cannot give a precise yes/no. In an exam, you would be expected to compute: fuel remaining = 1,150 - (30 + fuel used). Minimum required = (trip fuel remaining + 150 + 0.08 × trip fuel remaining) + 21 contingency + 180 alternate + 450 final reserve. If fuel remaining is less than this sum, divert. Since the problem lacks fuel used, the correct answer is to state the formula and note that the decision hinges on actual fuel remaining at the diversion decision point. Operationally, with 1,150 kg at startup and a total planned fuel of 420+30+21+180+450 = 1,101 kg, there is only 49 kg extra. The extra 15 minutes and anti-ice penalty will almost certainly exceed that margin, so a diversion to Limbang or return to Brunei is prudent. The minimum fuel required to continue to Miri from the present position is likely greater than the fuel remaining, so diversion is required. The model answer should emphasize that the planned fuel had little margin and the added factors make continuation unsafe.
2. If you divert to Limbang, what ATC communication and clearance readback steps are required, and what weather minima apply for the VOR/DME approach?
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On deciding to divert, you must inform ATC as soon as practicable: 'Brunei Approach, [callsign], diverting to Limbang, request clearance and heading.' ATC will issue a revised clearance, which you must read back in full, including heading, altitude, and any frequency changes. For the VOR/DME approach at Limbang, you must check the aerodrome operating minima for the approach category and aircraft performance. Since the ILS at Miri is unserviceable and visibility is 1,200 m, you must ensure Limbang's weather meets the VOR/DME minima (e.g., MDH and visibility). If Limbang is below minima, you must consider Brunei as alternate. The readback must include the clearance limit, route, altitude, and any speed restrictions. You should also request the current Limbang weather and approach type. If no approach is available, declare an emergency. The key is to not descend below minima without visual reference and to keep ATC informed of your intentions.