Why commercial aircrafts are flying at an altitude of 25000 - 35000 feet

because the air is thinner which provides less drag resistance. and the jet stream isnt as powerful at altitude

This is the Altitude that for many reasons can be very good for the Aviation industry.
11 reasons:

1. Burn Less Fuel: The air is less dense so therefore it has to use less fuel.

2. Because the air is less dense the Aircraft moves through the air much faster, almost at the speed of sound. At lower altitudes it cannot go as fast because of the drag from the dense air.

3. Fly Above most of the Severe Weather.

4. Comfortable for Passengers as the Aircraft cruises above much of the turbulence.

5. Less noise for the persons on the ground.

6. In case of engine failure the aircraft can glide to other airports safely as there is time for the pilots to plan an emergency landing.

7. Dont have to worry about obstacles on the ground that go as high as 12,000 feet (mountains).

8. Navigation is easier by ground navigation equipments as they r less restricted to terrain.

9. The pilot & passengers can join the mile high club if the want to.

10. If fuel has to be dumped for an emergency landing it can evaporate before reaching the ground.

11. The Jet can hitch a ride on the Jet Stream Air at that Altitude. Jet streams move as fast as 200kts so a jet moving at 400 kts will be moving over the ground at 600kts. Hmmmm... less fuel, less time, happy passengers & more money for Airlines.

It is cheaper to fly that high.

safety

fuel efficient

All Commercial flights must be under IFR or instrument flight rules (My friend calls it: l Follow the Road in the sky), which means that they must fly using the aircraft instruments only & they r being watched & told where to go & what to do by the flight centers controlling the aircrafts in the skies.
Federal Government here in the US has mapped the skies with imaginery points identified with aircraft instruments & they make everyone fly from one point to another when they r flying under instrument rule or IFR. These sky roads or vectors r then published monthly by the feds for every one to use. there r low altitude & high altitude IFR charts. Most smaller aircrafts unable to fly fast & at high altitude use the low altitude charts to fly IFR. Larger aircrafts use the high altitude IFR chart.

Prior to any flight the pilot in charge always have to perform a flight planning which is to familiarize him/her-self with the route of flight, altitude, weather/wind conditions & the airports.

Because of the speeds most commercial aircrafts r flying (400-500 miles per hour) they dont want to be at low altitude running into many small aircrafts flying at 100-200 miles per hour. So they go up to an altitude that has everyone flying at about the same speed & they follow each other. The altitude also is chosen for having less turbulance & most tail wind which makes the aircraft fly faster with less engine power which then saves them fuel & money.

So, saftey, economics ($$) & time (fly faster & get there faster) r some of the reasons.

--Better fuel efficiency.



Commercial flights do not have to be under IFR.

A pilot flying under IFR does not have to fly using the aircraft instruments only.

ATC does not have radar contact with some IFR aircraft.

ATC does not make all IFR traffic fly between waypoints.

Airways r not vectors.

High & low altitude IFR enroute charts r not published monthly.

Faster aircraft overtake slower ones all the time.