The Last Torque on the Second Night Shift

Factors present

• Time awake: ~13 h 40 min since 14:00, with a further 3.5 h of shift remaining.
• Sleep restriction: 4.5 h before the first night shift - a debt carried into the second.
• Circadian low: 03:00–05:00 sits in the window of circadian low, when alertness, vigilance and body temperature are at their minimum.
• Shift pattern: a second consecutive night gives only partial circadian adaptation; the body clock is still set for sleep.
• Stimulant use: caffeine masks subjective tiredness without restoring performance and can disturb the sleep that is needed afterwards.

How they interact The effects are not additive in a simple way - sleep debt plus long time awake plus the circadian trough produce a steeper decline than any one alone. The mechanisms that matter for this task are reduced vigilance, slowed responses and, critically, reduced working memory capacity. A torque sequence is a working-memory task: keep four bolts, one value, one order in mind while executing. Working-memory lapses produce omissions and repetitions.

Objective evidence Re-reading the same paragraph three times and re-verifying an already verified figure are compensatory checking behaviour - the technician is losing confidence in his own memory. Subjective self-assessment ('I'm fine') is a poor indicator; these observable behaviours are better. The task also has a defined second-person requirement that is currently unmet.

Decision: stop the task and hand it over. Reasoning, in order of weight:

1. A second person is required to confirm the wrench setting. That cannot be satisfied now, so continuing is a procedural stop before it is even a fatigue decision.
2. A partially torqued bolt group is a hazardous physical state - worse than an untouched one, because the next person may assume it is complete.
3. The observable signs of degraded performance are present. The moment to intervene is before the error, not after.
4. 'To avoid a handover' is a commercial/administrative convenience. It does not outweigh the risk, and the shift leader should say so explicitly and, if needed, escalate a departure delay to the maintenance manager.

Handover content

• Aircraft registration and exact task/step status: bolts fitted and hand-tight, sequence not started, not torqued.
• Torque wrench identification, calibration status and the value it must be set to; tool control - the wrench should be removed from the aircraft area or tagged.
• Parts, consumables and any removed items; what was disturbed.
• Duplicate inspection status.
• Face-to-face plus written, both parties sign, and where possible the incoming person physically verifies the state rather than taking it on trust.

Do not start a new high-attention task in the last hour of a night shift.

Because familiarity is exactly the condition under which the relevant errors occur. Highly practised tasks are executed in a skill-based, largely automatic mode; conscious monitoring of each step drops, and the action sequence is driven by expectation rather than by the card. Under interruption or fatigue, the step that gets dropped is typically the one that does not fit the expected sequence - an omission, not a wrong action.

'One hundred times' also means one hundred chances for the procedure to have quietly drifted away from the manual and still produced an acceptable outcome, which is how local norms form.

Finally, it is a claim about the past, not about the present state of the person making it. The relevant question at 03:40 is what his performance is now, and the re-reading and re-checking already answer that. In a just-culture sense, experience is not a defence for anyone; the defence is the procedure and the independent check.