Block Fuel

Block Fuel: 5% Verses 5 Minutes Verses 3% – Contingency Fuel

When we are doing our Block Fuel questions, we need to read the question carefully to determine what amount of contingency is required. We normally use 5% of trip fuel or 5 minutes of holding fuel @1500 ft overhead the destination aerodrome – whichever is the GREATER.
If we have an ERA (nominated for fuel purposes) we can drop the requirement to 3% or 5 mins – whichever is the GREATER.

If your trip time is short (under 2 hours), then there is a high probability that 5 minutes will be greater than 5%.

Let us have a look at a few questions:

1. For a jet aircraft, given:

1. Taxi Fuel 500 kg
2. Trip Time 7 hrs
3. Average Trip Fuel Consumption 9000 kg/hr
4. Destination Holding Fuel Flow 8500 kg/hr.
5. Alternate Holding Fuel Flow 8000 kg/hr
6. Alternate Fuel 10200 kg

What is the minimum Block Fuel required?

• Taxi Fuel 500 kg
• Trip Fuel (7 x 9000) 63000 kg
• 5% contingency (0.05 x 63000) 3150 kg (use)
• 5 mins (5 ÷ 60 x 8500) 708 kg
• Alternate Fuel 10200 kg
• Final Reserve (0.5 x 8000) 4000 kg
• Total 80850 kg

With this question we need the full 5% as it is a long flight where 3150 kg is greater than 708 kg.

2. For a jet aircraft, given:

1. Taxi Fuel 600 kg
2. Trip Fuel 7200 kg
3. Alternate Fuel 4380 kg
4. Destination Holding Fuel Flow 6500 kg/hr
5. Alternate Holding Fuel Flow 6000 kg/hr

What is the minimum take-off fuel?

• Taxi Fuel N/R
• Trip Fuel 7200 kg
• Contingency (0.05 x 7200) 360 kg
• Contingency (5 ÷ 60 x 6500) 542 kg (use)
• Final Reserve 3000 kg
• Total 15122 kg

We must be careful with this question as they do not give us a trip time but by looking at trip fuel and holding fuel flows, we can deduce that the trip time is under 2 hours. The other thing is we were asked for, is minimum take-off fuel and not Block Fuel so do not need taxi fuel.

3. An airline is scheduled to operate a commercial flight under IFR to an aerodrome with a single runway using a MRJT aircraft. A valid En-route Alternate (ERA) has been selected for contingency fuel purposes.
Given the following planning data, what is the minimum Block Fuel for the intended flight?

1. Taxi Fuel 700 kg
2. Take-off and climb 1500 kg
3. Cruise Fuel 9600 kg
4. Holding Fuel Flow (Dest + Alt) 4000 kg/hr
5. Descent 500 kg
6. Instrument Approach 1200 kg
7. Alternate Fuel 2500 kg

• Taxi Fuel 700 kg
• Trip Fuel (1500 + 9600 + 500 + 1200) 12800 kg
• Contingency (0.03 x 12800) 384 kg (use)
• Contingency (5 ÷ 60 x 4000) 333 kg
• Alternate Fuel 2500 kg
• Final Reserve (0.5 x 4000) 2000 kg

18384 kg

This time we need to use the 3% contingency as we have an ERA nominated and we must also be careful to add up all the components of trip fuel: take-off and climb, cruise, descent, and approach.
It is possible that with this type of question that 5 mins could be greater 0200Kg than 3%.