Hydraulic Failure After Take-off on a Twin-Jet
A twin-engine transport has just rotated from a sea-level runway at maximum take-off mass with flaps 5. During gear retraction the flight crew notes the left hydraulic system low-pressure warning, followed by loss of the left gear door indication and slow gear retraction. The right system pressure remains normal. The aircraft has three hydraulic systems: left (engine 1 driven pump plus electric backup pump), right (engine 2 driven pump plus electric backup pump), and centre (two electric pumps, used for gear and flaps). The centre system is not pressurised because its pumps are load-shed until the gear is up. The left system also powers the left thrust reverser and the outboard spoilers. No fire or smoke warnings are present. Weather is fine, and the departure aerodrome has a 2400 m runway with a 400 m stopway. The crew must decide whether to continue, return, or hold.
1. Explain the hydraulic and gear-retraction consequences of losing the left system at this moment, and state whether the centre system can be relied on to complete retraction.
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The left system supplies the left engine-driven pump. Its loss means the left gear door actuator and the left-side gear unlocking mechanism may be slow or inoperative, depending on whether the gear is mechanically sequenced or hydraulically sequenced. The centre system is the primary gear and flap system, but it is load-shed until the gear is up, so it is not available at this instant. The right system is independent and remains pressurised. Therefore the crew should not expect the centre system to rescue the retraction immediately; they should expect an asymmetric or incomplete retraction and a possible gear-door disagree. The correct judgement is to treat the gear as not reliably retracted, avoid accelerating above the gear-extended limiting speed, and plan a return rather than continue. The left thrust reverser is also affected, which reduces stopping margin on return, but the 2400 m runway plus 400 m stopway is generous. The key point is that a single-system loss during a sequenced gear cycle is a configuration problem, not merely a pressure warning.
2. Using the runway data, assess the stopping margin if the crew returns immediately with the gear possibly still extended and the left reverser unavailable.
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With the gear extended, the aircraft is in the landing configuration early, so the approach and landing distance is based on the gear-down, flap-5 landing mass, which is below maximum take-off mass because fuel has been burned. The 2400 m runway plus 400 m stopway gives 2800 m of usable distance. The loss of the left reverser removes one source of deceleration, but reversers are not credited in the certified landing distance in most cases; they are an additional margin. The dominant factors are the landing mass, the runway condition (dry), and the fact that the aircraft is already configured. The crew should compute the actual landing distance with the flight manual data for the actual mass and add the 15% factored margin. On a dry 2400 m runway, a gear-down landing at a mass well below maximum take-off mass should leave a comfortable margin. The judgement is that a return is safe, but the crew should fly a normal approach, use full available braking, and not rely on the failed reverser. If the gear cannot be confirmed down and locked, a low pass or tower confirmation should precede landing.
3. State the immediate crew actions and the decision logic that distinguishes continuing from returning.
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Immediate actions: maintain aircraft control, do not retract the gear further if it is jammed, select the gear down if retraction is incomplete, and confirm the gear position visually or by tower. Reduce speed to the gear-extended limit if the gear is not confirmed up. Notify ATC and request a return. The decision logic is: if the gear is confirmed up and locked and the left system loss has no other adverse effect, continuing may be acceptable with a diversion to a suitable airport. If the gear is not confirmed up, or if there is any asymmetry, the aircraft must return because the drag and configuration penalties make a long flight unacceptable. The absence of fire or smoke means there is no immediate emergency, so a controlled return is appropriate. The crew should also consider the left reverser loss for the landing roll and brief for a possible asymmetric reverse. The final decision is return, because the gear state is uncertain and the departure airport has adequate length.