What is the approximate engine starter cutout speed (as a percent of N2) for the NG?

What is the approximate engine starter cutout speed (as a percent of N2) for the NG?

• A. 56% N2
• B. 60% N2
• C. 52% N2
• D. 58% N2

Answer: (A)

Starter cutout speed is the point at which the engine’s starter automatically disengages after accelerating the high‑pressure spool (N2) to a speed where ignition and stable light‑off can be achieved. For the Boeing 737 NG with CFM56‑7B engines, the design target is in the mid‑50s percent N2, with 56% N2 being the typical approximate value used in standard start procedures. This speed provides enough momentum for reliable ignition while protecting the starter from overuse or overspeed. Other options sit outside the usual window: a value around 60% is higher than the common cutout for normal starts, and values around 52% or 58% are not as close to the standard mid‑50s target. In practice, environmental factors like temperature and bleed air conditions can shift the exact cutout a notch, but 56% N2 is the representative starting specification for the NG.

Starter cutout speed is the point at which the engine’s starter automatically disengages after accelerating the high‑pressure spool (N2) to a speed where ignition and stable light‑off can be achieved. For the Boeing 737 NG with CFM56‑7B engines, the design target is in the mid‑50s percent N2, with 56% N2 being the typical approximate value used in standard start procedures. This speed provides enough momentum for reliable ignition while protecting the starter from overuse or overspeed.

Other options sit outside the usual window: a value around 60% is higher than the common cutout for normal starts, and values around 52% or 58% are not as close to the standard mid‑50s target. In practice, environmental factors like temperature and bleed air conditions can shift the exact cutout a notch, but 56% N2 is the representative starting specification for the NG.