What is the significance of the 'TGT exceeds 851 % TOT' criterion in abort start?

• A. It signals an abort if the TGT exceeds 851% TOT
• B. It indicates a successful start
• C. It indicates cross-bleed start is required
• D. It indicates engine has variable geometry

Answer: (A)

During start, turbine gas temperature is watched closely to protect the engine during the fragile light‑off and acceleration phase. A high TGT that pushes well past the safe limit triggers the engine protection logic to abort the start before damage can occur. The 851% TOT threshold is that safeguard line: if the TGT exceeds this limit, the procedure calls for stopping the start to prevent overheating or a hot/start condition from causing compressor damage or structural stress.

In practice, you want the TGT to ascend smoothly as RPM increases and fuel flow is introduced. If it spikes beyond the abort limit, it usually means the flame hasn’t established properly or heat is rising too quickly without wheel speed catching up, so aborting is the prudent action. The other options don’t describe this protective signaling: a successful start would require the temperature to stay within limits, cross-bleed start is a method choice rather than a temperature limit, and variable geometry is a hardware feature not dictated by this temperature criterion.