ETOPS one-engine-inoperative diversion and equal-time point
A twin-engine jet is dispatched under ETOPS 120 min on an oceanic crossing. At a point 500 NM from en-route alternate ALFA and 700 NM from alternate BRAVO, the crew shuts down one engine. OEI cruise TAS is 380 kt. The wind gives a ground speed of 300 kt toward ALFA and 400 kt toward BRAVO. Fuel flow in the OEI configuration is 2,600 kg/h. Current fuel is 8,500 kg. The final reserve is 900 kg, and an approach allowance of 150 kg must be added at either alternate. ALFA is ahead on the route; BRAVO is behind. The commander must choose a diversion and confirm that the ETOPS segment is not exceeded. No other suitable alternate is available.
1. Compute the time and fuel to each alternate, including final reserve and approach allowance, and recommend which alternate to use.
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To ALFA: time = 500/300 = 1.667 h = 100 min; fuel = 2,600 × 1.667 = 4,333 kg; total required = 4,333 + 900 + 150 = 5,383 kg; margin = 8,500 − 5,383 = 3,117 kg.
To BRAVO: time = 700/400 = 1.75 h = 105 min; fuel = 2,600 × 1.75 = 4,550 kg; total required = 4,550 + 900 + 150 = 5,600 kg; margin = 2,900 kg.
ALFA is better: it saves 5 min and 217 kg of fuel, and leaves the larger margin. Choose ALFA.
2. Determine whether the present position is before or after the equal-time point between ALFA and BRAVO. Explain the result.
Read the worked answer
Let y be distance flown from the present position toward ALFA. At the ETP, time to ALFA equals time to BRAVO:
(500 − y)/300 = (700 + y)/400
4(500 − y) = 3(700 + y) 2,000 − 4y = 2,100 + 3y −100 = 7y y = −14.3 NM.
The negative sign means the ETP is 14.3 NM behind the present position. The aircraft has already passed the ETP toward ALFA, so ALFA is the correct diversion. This agrees with the fuel comparison.
3. Verify ETOPS 120-minute compliance for the chosen alternate. What happens if the headwind increases so that the ground speed toward ALFA falls to 290 kt?
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At 300 kt, ALFA is 100 min away, which is within the 120-min approval. If GS falls to 290 kt, time = 500/290 = 1.724 h = 103.4 min, still within 120 min. Fuel becomes 2,600 × 1.724 = 4,483 kg; total required = 4,483 + 900 + 150 = 5,533 kg; margin = 8,500 − 5,533 = 2,967 kg. The diversion remains legal and fuel-sufficient, though the margin is reduced. The crew should continue to monitor the ETOPS time and fuel; if the time exceeded 120 min or the margin fell below the final reserve, another suitable alternate would be required.