Holding at Night: Fuel Priority and the Decision Point
At 2210 local time a cargo turboprop is holding at FL180, 18 minutes from its destination. The crew reported for duty at 1500 and have flown four sectors; the captain has been awake since 0500. The destination weather is at the ILS minima with the cloud base falling and a thunderstorm cell 5 NM west of the field; the terminal forecast gives a 40 % probability of visibility below minima for the next hour. ATC advises a landing delay of 25 to 30 minutes. Fuel on board is 2 400 kg; total fuel flow is 2 400 kg/h. An approach and landing at the destination uses 200 kg, the alternate 20 minutes away requires 800 kg, and the final reserve is 1 200 kg (30 minutes). The first officer says the company will not thank them for a diversion and suggests accepting the hold.
1. Convert the fuel state to time, and determine which standard fuel phrase applies and when.
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Conversion. 2 400 kg/h = 40 kg/min, so 2 400 kg = 60 minutes of fuel.
The three figures that matter
- Land at destination: 200 (approach and landing) + 1 200 (final reserve) = 1 400 kg, i.e. 35 minutes. You have 60 minutes, so there is 1 000 kg, or 25 minutes, of discretionary fuel - exactly the length of the advised hold.
- Divert, no approach: 800 + 1 200 = 2 000 kg, leaving only 400 kg = 10 minutes.
- Accept a 25-minute hold and land with exactly 1 400 kg; accept a 30-minute hold and land with 1 000 kg, which is 200 kg below the final reserve.
The phrases (ICAO)
- MINIMUM FUEL - the aircraft is committed to land at a specific aerodrome and any change to the present clearance would result in a landing below the final reserve. That is the state reached at about 1 400 kg, i.e. after about 25 minutes of holding.
- MAYDAY FUEL - the fuel state requires priority because the aircraft is expected to land with less than the final reserve. A 30-minute hold produces that state.
So the current fuel permits neither phrase yet, but accepting the full hold puts the aircraft into a MAYDAY FUEL state by design. That must not be accepted silently.
2. Where is the decision point, and what should the crew do now?
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Decision point. The diversion option closes after 10 minutes of holding (400 kg). Beyond that, the aircraft is committed to the destination whatever the weather does.
The situation as offered
- A 25-minute hold leaves exactly the approach fuel plus the final reserve: no alternate, no second approach, no go-around margin, with the weather at minima and a thunderstorm 5 NM west.
- A 30-minute hold breaches the final reserve outright.
Correct action now
- Tell ATC the fuel state and request either an immediate approach or a-specific short delay - ask for the delay in minutes, not 'a while'.
- If an immediate approach is not available, divert now, while the 400 kg of diversion fuel still exists. This is the fuel point of no return.
- If the crew elects to commit to the destination, they must say so: declare MINIMUM FUEL, and upgrade to MAYDAY FUEL if the expected landing fuel falls below 1 200 kg. Declaring is a commander's decision and does not require company agreement.
- Do not accept a clearance the aircraft cannot comply with. A clearance is not a commitment to hold until the fuel runs out.
The crew should be monitoring fuel against the 2 000 kg and 1 400 kg figures continuously, not working it out once the hold has already been accepted.
3. What human factors are at work here, and what should be communicated and recorded afterwards?
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Human factors
- Fatigue: awake since 0500 and now 2210 is about 17 hours awake; duty has run about 7 hours 10 minutes over four sectors, at night, in deteriorating weather. Fatigue degrades exactly the skills needed here: arithmetic under load, monitoring, and the willingness to reverse a plan.
- Plan-continuation bias: the crew have planned to land here, and the destination is 'almost there'. The thunderstorm and the TEMPO probability are being discounted.
- Social and commercial pressure: the first officer's remark about the company is a classic external pressure cue. The counter is an explicit decision rule agreed before the approach: 'we divert at X kg, whatever the schedule'.
- Authority gradient: the first officer has raised a concern and then withdrawn it. The captain should invite the concern back and answer it on the numbers, not the schedule.
Communication and recording
- Standard phraseology to ATC: MINIMUM FUEL or MAYDAY FUEL, with the fuel in minutes, and a clear statement of intentions.
- Advise company operations of the diversion and the reason.
- After landing: fuel report, fatigue report if relevant, and a safety report if the final reserve was entered or a fuel emergency was declared. The point of the report is the decision made 10 minutes earlier, not the landing.