The Checklist Interruption
During the before-start checklist, the ground engineer interrupts the first officer to discuss a fuel figure. The first officer answers, returns to the checklist, and continues from memory: 'Flaps, set; trim, set; brief, complete.' The captain, also distracted by the engineer, confirms each item. In fact the take-off brief was never completed, and one performance figure was never cross-checked. The aircraft departs normally. Nothing is noticed until the debrief, when the captain cannot recall the take-off speeds being confirmed. The flight was uneventful, but the crew realise the checklist was completed 'from the flow' rather than from the card.
1. Explain the error mechanism and why the outcome was safe by luck rather than by design.
Read the worked answer
The interruption broke the checklist sequence, and when the first officer returned they resumed from memory rather than from the point of interruption. Memory for a routine sequence is reconstructive: the crew produced a plausible, fluent version of the checklist that matched their expectation of a normal start. The captain's confirmation was equally expectation-driven, because both were distracted. The flight was safe because nothing abnormal occurred, not because the defences worked. Had a performance figure been wrong, the crew had no independent check to catch it. This is a latent failure waiting for an occasion.
2. What is the correct procedure after an interruption, and how should the crew have handled the engineer?
Read the worked answer
The correct response is to stop, mark the interruption, and on returning restart the checklist from a defined point, usually the beginning of the affected checklist or the last confirmed item, reading from the card. The engineer's query should have been deferred until the checklist was complete, or handled by the captain while the first officer finished the card without interruption. The crew should also have verbally confirmed the take-off performance figures against the load sheet and the runway analysis, rather than accepting a memory-based 'brief complete'.
3. What does this case show about the limits of routine and the value of read-and-do?
Read the worked answer
Routine is efficient but fragile: it allows a crew to produce the appearance of a completed checklist without the content. Read-and-do checklists exist precisely because memory and expectation are unreliable under interruption. The crew's fluency was the warning sign, not the reassurance. Operators should design checklists and procedures that force a return to a defined point after interruption, and training should include interrupted-checklist scenarios so that crews practise the recovery rather than only the normal flow.