The Pratt & Whitney JT15D-5 turbofan engine operating limit for engine start if the ITT is 550 to 600 degrees C is a maximum of:

• A. 2 seconds
• B. 6 seconds
• C. 8 seconds
• D. 4 seconds

Answer: (D)

During engine start, the ITT limit governs how long fuel and ignition can be applied before risking heat damage. When the indicated ITT is in the 550–600 C range, the safe starter-on duration is four seconds. This short interval reduces the chance of overheating the combustor and turbine parts and protects bearings and the starter from thermal stress. If ITT sits in that high range for more than four seconds, you’d abort the start to prevent damage. In lower ITT ranges, longer start times may be permitted, but with ITT in 550–600 C, the four-second limit is the guideline you follow.