What is the maximum altitude at which the APU can be started?

The maximum altitude at which the Auxiliary Power Unit (APU) can be started on a Canadair Regional Jet is 37,000 feet. This specification is important because it ensures that the APU can operate effectively and provide the necessary electrical power and bleed air for cabin pressurization or engine starting, even at high altitudes.

Operating at higher altitudes presents unique challenges due to thinner air, which can affect the performance of various aircraft systems, including the APU. The manufacturer's guidelines set this limit to ensure safe and reliable operation. Starting the APU above this altitude may compromise its functionality, leading to possible performance issues or system failures. Hence, being aware of the correct altitude limits helps pilots manage operations safely and effectively during flight.