Cold-morning hung start at Invercargill

This is a hung start turning into a hot start.

• Fuel off / thrust lever to cutoff now. With N2 frozen at 20 %, airflow through the engine is not increasing while fuel continues to burn. Stopping the fuel is the only way to stop the heat input. Waiting to see whether N2 picks up converts a hung start into a damaged hot section.
• Keep the starter engaged, within the 40 s limit. Motoring with fuel off pushes air through the combustor and turbine and carries heat away. EGT should peak almost immediately and then fall; that is the whole purpose of motoring rather than simply switching everything off.
• Watch EGT, not N2. If EGT keeps rising with fuel off, either fuel is still being delivered (a leaking fuel control, or a tailpipe fire) or the indication is lying. That is an evacuation and ARFF situation, not a troubleshooting one.
• Do not re-engage the starter inside the duty cycle (60 s off). Starter and starter-generator limits protect the starter from overheating; the second attempt is made with a cooler starter and, if at all possible, an external power source.
• Record the peak EGT, the N2 at which acceleration stopped, and the duration before doing anything else. That number drives the maintenance decision.

Cold-soaked engine, cold oil, and a battery that had already started one engine. At 0 °C the battery's capacity and its voltage under a heavy crank are both reduced; 24.5 V open-circuit may be well under 20 V while cranking. The starter-generator therefore produces less torque, N2 accelerates more slowly, and the fuel control introduces fuel on its schedule before there is enough airflow for the fuel being burned. The result is heat going into a turbine that has too little air to carry it away - the classic hot start.

Motoring achieves three things:

• it purges unburned fuel from the combustor and tailpipe before it can ignite and cause a tailpipe fire;
• it provides cooling air across a turbine still being heated by soak-back from the hot section;
• it brings the starter and engine back to a known temperature state so the next attempt starts inside limits.

Prevention is the same reasoning in reverse: external power or a healthy battery, preheat where available, and abandoning the start early if N2 acceleration is sluggish - ideally before fuel is introduced.

880 °C exceeds the 850 °C start limit and sits inside the 900 °C/2 s window only briefly - in practice the duration will have been seconds, not the one or two allowed. That is an exceedance and must be treated as one.

• Technical log entry with peak temperature, time above the limit, the N2 at the time and the OAT. 'Start was hot' is useless to an engineer.
• Maintenance inspection to the engine manufacturer's exceedance chart. These charts use peak and duration to define whether the action is a borescope, a hot-section inspection or a log entry only. The engineer and the approved maintenance organisation make that call, not the pilot.
• The aircraft is not dispatchable until that release is given. A hot start can leave burnt blade tips, distorted nozzle guide vanes, damaged seals and lost EGT margin. The damage may not show at the next start or run-up; it will show on a hot day as lost margin, or later as a blade failure.
• Find the cause. If the battery or starter caused it, the next start will be the same or worse. Rectify before departure and report the defect so the operator can check the battery and start system.
• Capture it in the operator's defect/occurrence reporting system as the company procedure requires.