ILS Approach with a Late Runway Change and Fuel Pressure Fluctuation
You are on an IFR arrival into Bahrain at night in a twin-engine piston aircraft. You are cleared for the ILS to runway 30R and have been vectored to a 12 NM final. At 8 NM the tower offers runway 30L instead because of a disabled aircraft on 30R. You accept, but the new approach requires a repositioning turn and a re-intercept. As you begin the turn, the left engine fuel pressure gauge fluctuates and the left engine runs rough for about 5 seconds before recovering. You have 45 minutes of fuel remaining above your alternate reserve, and the weather is 2,000 ft broken, 6 km visibility, wind 300/12 kt.
1. How do you handle the runway change and the engine anomaly together?
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The two events interact, so handle them in a fixed priority order: aviate, navigate, communicate.
First, aviate: maintain the aircraft's flight path and do not allow the runway change to distract you from attitude and speed control. If the repositioning turn would put you inside the final approach course or unstable, it is entirely acceptable to tell the tower you cannot accept the change and request vectors for a new approach.
Second, manage the engine: a transient rough run with fluctuating fuel pressure may indicate fuel contamination, a failing fuel pump, or an air lock. Treat it as a warning. Select the other tank if the system allows, keep the engine monitored, and be prepared for a shutdown. At night in IMC with a 2,000 ft ceiling, an engine failure on approach is a serious event; a go-around and a hold to diagnose may be safer than continuing.
Third, communicate: tell Approach or Tower that you have an engine anomaly and need vectors or a hold to assess. Do not accept a late runway change that increases workload while an engine is misbehaving.
The judgement is that the runway change is optional and the engine anomaly is not; you decline the change if it compromises your ability to manage the engine.
2. What does the fuel pressure fluctuation suggest, and what checks do you make?
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A fluctuating fuel pressure with a brief rough run suggests an interruption in fuel supply rather than a purely electrical indication. Possibilities include:
- Fuel contamination or water in the tank, causing intermittent starvation.
- A failing engine-driven fuel pump, with the electric boost pump masking the problem intermittently.
- A vapour lock, less likely at night in cool air but possible if a fuel line is close to a heat source.
- A faulty pressure transducer or gauge, which must be ruled out but not assumed.
Checks:
- Confirm fuel quantity and balance, and select the other tank if the system permits.
- Turn on the electric boost pump if not already on, and observe whether the pressure stabilises.
- Check mixture, throttle, and any fuel selector position for inadvertent movement.
- Monitor engine parameters: fuel flow, EGT, RPM, and manifold pressure.
- If the roughness returns or pressure falls again, plan for an engine shutdown and a single-engine approach, and consider diverting to an airport with better weather and services.
The examiner is testing whether you diagnose a transient warning rather than dismiss it because the engine recovered.