Turbine Engine Start Abort Decision Away From Base
A twin-engine turboprop is at a remote strip 900 km from its maintenance base. On the first start of the day, the right engine lights off normally, but exhaust gas temperature rises faster than usual and the start is aborted at 780 °C, above the normal start peak of about 720 °C but below the published start limit of 850 °C. The starter was replaced two days earlier after a slow-cranking report. Battery voltage during the start was 24.1 V on a 24 V system, and outside air temperature is −5 °C. The crew has one spare starter but no borescope and no maintenance support on site. The schedule requires departure within four hours.
1. Analyse the likely cause of the high start EGT and explain whether the abort was appropriate even though the limit was not exceeded.
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The start peaked at 780 °C, within the 850 °C limit, but well above the 720 °C normal peak. The key clue is the recent starter replacement plus a battery reading of 24.1 V on a 24 V system during the start. A starter that cranks slowly, or a battery whose voltage collapses under load, reduces the airflow through the engine during light-off while fuel scheduling remains roughly unchanged. The result is a richer, hotter start with a higher EGT peak. Cold soak at −5 °C also raises fuel viscosity and reduces battery capacity, both of which worsen cranking speed.
The most likely causes, in order:
- Low cranking speed from a marginal battery or incorrect starter installation (shimming, wiring resistance, or wrong part number).
- Fuel scheduling issue such as a partially stuck fuel control or a hot-start tendency from a miscalibrated fuel unit.
- Ignition or igniter degradation causing late light-off and a longer fuel-soaked start.
The abort was appropriate. The published limit is a certification maximum, not a target, and a start trending 60 °C above normal is a warning of a developing problem. Continuing the start would risk a hot start and possible turbine damage that cannot be inspected at a remote strip.
2. Recommend the actions to take before the next start attempt and the criteria for declaring the aircraft fit to depart.
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Before the next attempt:
- Load-check the battery or, better, use an external power cart so cranking speed is not battery-limited. A 24.1 V reading during cranking on a 24 V system is low and should be verified with a proper capacity test.
- Verify the replacement starter is the correct part, correctly shimmed, and that its wiring and ground connections are clean and tight.
- Confirm the igniters are serviceable and check for any fuel residue at the exhaust that would suggest a previous wet start.
- Review the engine start procedure for cold weather: correct fuel priming, correct use of any start enrichment, and the published minimum cranking speed.
Departure criteria:
- A start with an EGT peak at or near the normal 720 °C value, achieved with adequate cranking speed.
- No abnormal noise, no hung start, and normal acceleration to idle.
- If the EGT peak remains elevated or rises further, the aircraft does not depart. Without a borescope, a hot-section inspection cannot be done on site, so a repeat high start means a maintenance ferry or repair team, not a schedule-driven departure.
I would also record the aborted start in the engine log with the peak EGT and the reason, so the base can trend it.
3. Discuss the human and organisational pressures in this scenario and how they should be managed.
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The four-hour schedule is the dominant pressure, and it is exactly the kind that produces a departure with an unresolved engine anomaly. The crew has already done the right thing by aborting a start that was within limits, which shows good judgement, but the presence of a spare starter on site creates a temptation to change parts without diagnosing the cause. Changing the starter when the battery is marginal would waste the part and could introduce a new fault.
The recent starter replacement also creates a confirmation bias: the crew may assume the new part is good and look elsewhere, or assume it is faulty and replace it again without checking cranking speed and voltage. A structured approach avoids both errors.
Management actions:
- Treat the schedule as subordinate to the engine limits and to the no-borescope constraint.
- Document the anomaly and the reasoning for the decision, so the decision is defensible.
- Contact the maintenance base for engineering advice before spending the spare part.
- If departure is delayed, communicate early to the operator rather than allowing schedule pressure to build at the last minute.
A crew that aborts a start at 780 °C and then departs after an undocumented second start has gained nothing. The record and the diagnosis are what make the eventual departure safe.