What is the maximum altitude at which flaps/slats may be extended?

What is the maximum altitude at which flaps/slats may be extended?

• A. 10,000 ft
• B. 20,000 ft
• C. 25,000 ft
• D. 30,000 ft

Answer: (B)

Extending flaps and slats changes the wing’s lift and drag and must be done within the airplane’s certified operating envelope. The systems that deploy these devices are tested and approved to work reliably only up to a certain altitude, where the air is still dense enough and the aircraft has adequate performance margins. For the ERJ 175, that certified limit is 20,000 feet. Above this altitude, extending flaps or slats is not approved because reliability and handling cannot be guaranteed in thinner air, and performance margins with the devices extended would be compromised. So the maximum altitude for flap/slat extension is 20,000 feet.

Extending flaps and slats changes the wing’s lift and drag and must be done within the airplane’s certified operating envelope. The systems that deploy these devices are tested and approved to work reliably only up to a certain altitude, where the air is still dense enough and the aircraft has adequate performance margins. For the ERJ 175, that certified limit is 20,000 feet. Above this altitude, extending flaps or slats is not approved because reliability and handling cannot be guaranteed in thinner air, and performance margins with the devices extended would be compromised. So the maximum altitude for flap/slat extension is 20,000 feet.