Diversion at the Fuel Limit
You are the pilot-in-command of a single-engine turboprop on an IFR flight from Confins (SBCF) to Brasília (SBBR), planned block time 1h20, with 2h50 of fuel on board at engine start. Thirty minutes out, Brasília ATIS reports a thunderstorm over the field, RVR 900 m, and windshear warnings; the tower advises holding is expected. Your alternate is Goiânia (SBGO), 90 NM west. You hold for 25 minutes at FL190, burning 380 kg/h, then are cleared for the ILS but go around at minima because of windshear and are told to expect another 20 minutes of holding. Final reserve for this aircraft is 30 minutes; you have 1h05 of fuel remaining.
1. Apply the fuel-planning logic of the RBAC to decide whether you may continue to hold for another approach or must divert now.
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The decision rests on protecting the final reserve, not on the total fuel figure.
- Fuel remaining: 1h05.
- Final reserve: 30 minutes.
- Fuel available for further holding plus the diversion to SBGO: 35 minutes.
- The diversion to SBGO (90 NM) at roughly 250 kt ground speed is about 22 minutes plus approach and landing, call it 28-30 minutes.
So if you accept another 20 minutes of holding, you land at SBGO with almost nothing above the final reserve, and any further delay (another go-around, a runway change, a vector) erodes it. The correct call is to declare minimum fuel now, request priority for the diversion, and land at SBGO. If the delay were to push you below the final reserve, you would upgrade to MAYDAY FUEL. The exam point is that the final reserve is inviolable and that a second approach into known windshear is not a legal substitute for a diversion decision.
2. What is the difference between declaring MINIMUM FUEL and MAYDAY FUEL, and which applies here?
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MINIMUM FUEL is an advisory: you are committed to landing at a specific aerodrome and any further delay would leave you below the final reserve. It does not give you priority and does not require ATC to do anything except be aware. MAYDAY FUEL is a distress call: you are about to land below the final reserve and require priority handling.
In this scenario you still have 35 minutes above the final reserve and a diversion of about 30 minutes, so you are not yet below reserve; you declare MINIMUM FUEL while requesting the diversion. If the diversion itself starts to consume the final reserve, for example because SBGO also goes below minima and you must hold again, you upgrade immediately to MAYDAY FUEL. The distinction matters because declaring MAYDAY FUEL prematurely is a misuse of a distress signal, while delaying it past the reserve is a fuel emergency.