Look-Alike Fuel Quantity Indicators: An Error Investigation
At 02:40, in the eleventh hour of a 12-hour night shift, a technician replaces a fuel quantity indicator. Two units sit side by side in the same open bin in stores: P/N 4021-01 (left) and 4021-02 (right). They share the same shell, connector and fixing holes; the only external differences are the last two digits on the label and the colour of one wire in the plug. The technician has been called away twice for ramp requests. The task card's duplicate-inspection box was signed at the start of the shift by a supervisor who has since gone home. The wrong unit is fitted and is caught during the post-installation functional test when the gauge reads full scale. Shift handover is verbal.
1. Classify the error and explain why calling it 'carelessness' is both inaccurate and unhelpful. Identify contributing factors at individual, team and organisational level.
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Classification
This is a skill-based slip/lapse in an experienced operator - the correct intention (fit the left indicator) was carried out with the wrong object. It is a look-alike parts selection error, not a knowledge failure or a deliberate breach.
'Carelessness' is unhelpful because it names a personality trait rather than a mechanism, and it implies that the fix is 'try harder'. Humans under time pressure and fatigue will mis-select similar items; the same conditions will produce the same error with the next technician. It also discourages reporting, which removes the data needed to fix the system.
Contributing factors
- Individual: 11th hour of a 12-hour night shift (fatigue, circadian low 02:00–04:00); task interrupted twice, so the mental 'place-keeping' was broken.
- Team: duplicate inspection pre-signed by a supervisor who then left - the defence existed on paper but not in reality; verbal-only handover loses the open-item status.
- Organisational: look-alike parts stored loose in one bin with no segregation, kitting or scanning; task card design allows a signature before the work; shift pattern and staffing did not protect the inspection.
2. Rank the corrective actions by effectiveness and justify the ranking.
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Ranked (most to least effective)
- Design / physical defences (error-proofing). Segregate the two part numbers into separate, clearly labelled locations; kit parts per work pack so only the correct unit is presented; introduce part-number scanning or barcode verification at issue and at fit. This removes the error opportunity instead of relying on attention.
- Independent verification at the point of fit. Duplicate inspection must be performed on completion, by a second person, against the part number marked on the unit - never pre-signed. This converts an undetected slip into a detected one.
- Procedural controls. Written shift handover listing open tasks and deferred items; task cards structured to require the part number to be transcribed from the work pack and then checked; interruptions managed by a 'stop and mark your place' rule.
- Training and awareness. Least effective on its own: it changes what people know, not the conditions they work under. It is only useful when it explains a design change and reinforces the verification routine.
Justification: detection and prevention layers must sit close to the error. A physical barrier works every time regardless of fatigue; attention works until the eleventh hour.
3. What should happen to the technician, and what should the organisation do with the finding?
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The technician
- The response should follow a just-culture principle: an unintentional slip, self-reported or openly disclosed, is treated as a system-learning event, not a disciplinary one. The pre-signed inspection by the supervisor, if it happened knowingly, is a different matter - an intentional deviation - and is handled separately under the organisation's procedures.
- The technician should support the investigation, describe the sequence honestly, and not be discouraged from reporting.
The organisation
- Raise a formal maintenance error investigation (e.g. a MEDA-style analysis) covering the individual, the environment, the task and the organisation.
- Check whether this is isolated or a trend: the same stores bin may have produced other mis-fits; audit pre-signed inspection boxes across other task cards.
- Fix the latent conditions: stores segregation, kitting, scanning, interruption management, handover format, and shift design for fatigue risk.
- Record the finding in the safety management system, share the lesson (without blame) with the shift, and monitor the effectiveness of the actions rather than assuming they worked.