Fourth Sector Fatigue on a Night Visual Approach
At 21:15 local a two-pilot crew is on the fourth sector of the day. The commander woke at 04:00 after about five hours' sleep, reported at 05:30, and the day has already included an unplanned two-hour ground delay. The first officer slept about three hours because of a new baby, says he feels "spaced out", and has just taken a 200 mg caffeine tablet. Both are cleared for a night visual approach to a 1 800 m runway with a 150 ft displaced threshold and rising terrain 1.5 NM before the threshold. There is no approach lighting and no radar. Weather is 4 000 m visibility, no cloud, calm wind. During the descent the commander notices that the first officer has set 1023 hPa on his altimeter instead of the aerodrome QNH of 1003 hPa, and has misread a clearance back for the second time. Company policy allows the commander to extend the 13-hour flight duty period by up to two hours; the crew is one hour into that extension.
1. Identify and rank the fatigue-related factors present and explain their specific effect on the crew's performance.
Read the worked answer
Ranked by significance here:
- Chronic and acute sleep loss. The first officer at three hours' sleep is carrying a sleep debt and is likely to be in a degraded state for vigilance, monitoring and self-assessment. Critically, the impairment is invisible to him: sleepy people consistently rate their own performance higher than it is.
- Time awake and time on task. The commander has been awake about 17 hours and on duty over 15 hours, with four sectors. Error rates, and specifically the rate of omission errors in monitoring and readback, rise steeply after about 16 hours awake - the altimeter and readback errors are exactly that signature, not carelessness.
- Circadian effects. 21:15 sits in the evening dip of the body clock, and the crew has been up since 04:00, so their circadian rhythm is out of phase with the duty. A night visual approach into an unlit runway is the highest-workload, highest-error task of the day, placed at the worst physiological moment.
- The disruptive ground delay removed their opportunity to rest and added unplanned time on duty.
- Caffeine produces alertness but does not restore judgement, and taken late it will disrupt the next sleep period - it treats the symptom while worsening the cause.
Key insight for the exam: none of these factors makes the crew legally unfit; they make the crew error-prone. The errors already observed are the evidence, and the decision must respond to the errors rather than to the roster.
2. What does the altimeter setting error mean for this approach, and what should the crew do?
Read the worked answer
The error. The pressure error is 1023 − 1003 = 20 hPa. At roughly 27 ft per hPa near the surface, the altimeter reads about 540 ft too high: the aircraft is 540 ft lower than the indication. On a visual approach to an unlit runway with rising terrain 1.5 NM before the threshold, that is a terrain and undershoot risk, not a paperwork issue.
Immediate action.
- Discontinue the visual approach (go around / break off) unless the aircraft is already in a position where a safe landing is assured - with terrain before the threshold, assume it is not.
- Cross-set both altimeters from the same source and cross-check the standby; confirm the QNH with the aerodrome and with the other pilot.
- Cross-check the indicated altitude against a known datum (airfield elevation on the ground, DME/height on the approach, radio altimeter) before re-attempting.
Wider reading. The altimeter error and the misread clearance are two failures of the same function - the first officer's monitoring and cross-check. The commander should treat this as a fatigue-driven error chain: take over the flying, use the autopilot and flight director to the lowest safe altitude, slow the tempo, and make every setting a challenge-and-response item. If a further error occurs, or if the crew cannot establish a stable, fully cross-checked approach, divert to an aerodrome with vertical guidance and better lighting rather than pressing on to a visual approach at night.
3. The commander wants to use the two-hour extension to complete the sector. Evaluate that decision and the legitimate mitigations.
Read the worked answer
Legality and safety are separated here. The extension is permitted by company policy, but permission is not an assessment. The commander must decide whether the crew, as they are now, can safely complete the approach and landing - and the evidence (three hours' sleep, 17 hours awake, a 540 ft altimeter error and a second readback error) says the barrier is already breached.
Legitimate mitigations:
- Stop and rest before the approach, if the aerodrome allows; even a short period of sleep on the ground materially improves performance, and sleep inertia must be allowed to clear before duty resumes.
- Hand the flying to the commander and fly a fully managed approach with vertical guidance, with explicit challenge-and-response on altimeter settings and clearances.
- Divert to an aerodrome where a precision or vertically guided approach with approach lighting is available.
- Delay the approach until both pilots confirm they are fit to continue.
Not legitimate: treating caffeine as a mitigation, treating "we're nearly there" as a reason, or using the extension because it exists. The extension is discretionary precisely so that it can be refused.
After landing: report under the operator's fatigue reporting scheme and the SMS, including the extension decision. Fatigue that shows up as undetected altimeter errors is a systemic finding for the flight-time limitation scheme, not a personal failing of the first officer - the roster put a night visual approach at the end of a 17-hour day.