By chance, we have just discovered this interesting article related to the general cruising altitude of commercial airlines, here is the summery:
- The “sweet spot” of flying is regarded as between 35,000 and 42,000 feet
- Money : heavier planes would fly lower, and lighter higher
(and provided that the plane has enough power for climbing)
fly higher – thinner air imposes less drag – travel more easily and therefore move faster and burn less fuel, saving money
- Range consideration : turbojet engine increases in specific range with altitude.
- Altitude↑, air den ↓ , TAS ↑
- OAT ↓ , inlet air temperature ↓ , specific fuel consumption ↓
- Engine RPM ↑ , specific fuel consumption ↓
- WX consideration : Troposphere – that is the atmospheric layer closest to the ground – is home to most of the world’s weather phenomenons. Usually measured up to 36,000 feet. Aircraft prefer life in/near the stratosphere, less WX phenomenons which means less turbulence.
- Avoiding Airborne traffic: High also means that aircraft are able to avoid other airborne traffic – e.g general aircraft (GA)/ light planes and helicopter
(provided that the plane with sufficient O2 supply for Crews and PAX)
- In the event of an emergency, pilots have much more time for taking action or related drills
- Noise abatement: environmental reasons – planes fly higher, lower noise delivery to the ground
For more details, please refer to the link below: