The Bleed Valve Return and the Instruction to Write 'No Defect Found'
Twenty minutes after a night departure from Lagos, the crew of a 5N-registered Boeing 737-800 gets a left bleed trip with a cabin altitude fluctuation, levels at FL200 and returns to Lagos, landing without injury or damage. Maintenance finds the high-pressure bleed valve had failed internally; the same valve had been replaced by the operator's own AMO only 40 flight hours earlier. The director of maintenance asks the certifying engineer to write 'ground test satisfactory - no defect found' so the event stays out of the airline's occurrence statistics ahead of an NCAA audit, arguing: 'It is an incident, not an accident, so neither the NSIB nor the NCAA needs it, and certainly not within 24 hours.' While checking the earlier paperwork the engineer sees that the valve change was signed by an engineer whose 737 type endorsement had expired. The aircraft is scheduled for a 06:00 departure and the tech log entry is still open.
1. Classify the occurrence and set out who must be notified, by whom, and roughly when.
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Classification first, because the reporting duty follows from it. Under the Annex 13 definitions, an accident involves death or serious injury, substantial damage, or the aircraft being missing or inaccessible. None of those apply here. An incident is an occurrence, other than an accident, associated with the operation of an aircraft that affects or could affect the safety of operations; a bleed failure with cabin altitude fluctuation and an air turnback comfortably meets that. Whether it escalates to a serious incident depends on the circumstances - for example, if pressurisation was actually lost or an emergency descent was flown - but the DOM's conclusion that 'incident therefore nothing is reportable' is wrong.
Reporting channels:
- The operator notifies the NCAA, the safety regulator, under the mandatory occurrence reporting requirements that implement Annex 19, and the NSIB, the accident investigation body established under the NSIB Act 2022, which investigates occurrences independently of the regulator.
- The operator's own occurrence reporting procedure sets the exact deadlines; accidents and serious incidents are notified immediately by the fastest available means, and incidents go by mandatory occurrence report within the prescribed short period.
- Because the failed valve had been replaced 40 flight hours earlier, the maintenance history is part of the report, and the State of Design or manufacturer may need the information for continuing airworthiness action.
An air turnback with a failed bleed valve and an open maintenance question is precisely the data the system exists to collect.
2. Assess the DOM's instruction. What should the engineer do, and what are the consequences of a false entry?
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The instruction is an invitation to falsify a maintenance record. 'Ground test satisfactory - no defect found' is factually false: a failed high-pressure bleed valve has been removed and its failure is the reason the aircraft returned. Writing it would misstate the aircraft's technical history, defeat the occurrence report and hide a repeat defect from the safety system.
The engineer should:
- Record the finding accurately, including the failure mode, part and serial number, and the 40-hour history.
- Preserve the valve and photographs; do not let it be scrapped or returned to service before investigation.
- Refuse the instruction and put the refusal in writing to the accountable manager and safety manager, not only to the DOM.
- Escalate to the NCAA if the pressure continues; the Act provides protection for safety reporting.
Consequences of a false entry: for the engineer, suspension or revocation of his licence, a financial penalty and possible prosecution for a false certification; for the AMO, action against its approval and a quality-system audit; for the AOC holder, enforcement action and a seriously weakened position at the coming audit. Just culture protects honest error and open reporting. It does not protect deliberate concealment, and a pattern of suppressed reports is treated far more harshly than the original defect.
3. What should be done about the lapsed type endorsement discovered on the earlier valve change?
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It must be handled as a compliance finding, not quietly corrected. The earlier release was signed by someone who did not hold a valid type endorsement for the aircraft at the time, which means the certification was made without the privileges required. That does not automatically prove the work was performed badly, but it does mean the release is invalid and the aircraft's airworthiness record is deficient.
Actions:
- Do not backdate, re-sign or overwrite the record. Preserve it and record the finding separately.
- Review all work certified by that person during the period his endorsement was not valid, and determine which aircraft and tasks are affected. Re-inspect where the quality of the work cannot be established.
- Notify the NCAA, ideally through a voluntary disclosure that sets out the extent of the problem and the corrective action. Voluntary disclosure, done fully and promptly, is treated more favourably than discovery by an inspector.
- Review why the roster and authorisation system allowed certification to continue with a lapsed endorsement, and fix the control.
The engineer should also connect this to the occurrence report: a repeat bleed-valve failure 40 hours after replacement may reflect workmanship, parts documentation or training, and the invalid certification is directly relevant to that investigation.