Hypoxia and Medicine

Why do ailiners have to fly at such (relatively) high altitudes?

Why not fly at say, 1000ft? wouldnt have to pressurize cabins and all that, and save fuel, and faster journeys too Also, when pilots land 777s and similar in really bad weather, does it take total concentration for them to land, or is it like 2nd nature for them?

Public Comments

1. They fly at higher altitudes due to the air being thinner making less drag which is an important factor against the principles of flight therefore making the flight more economic and they do pressurize the cabins...Usually the pilot lands via and "ILS" system Instrument Landing System and guides them IFR landing (non-visual approaches) or through bad weather...
2. Jet engines perform more efficiently, fuel-wise, at high altitudes, because the fuel burns almost 100% completely. At lower altitudes fuel is wasted because of inefficient burning.
3. We fly so high because it is efficient. The air is thin up there so the same airspeed produces less drag. Also, a jet engine, any engine for that matter, burns less fuel at high altitude. The combination of fuel and air mixed and injected into the combustion chamber remains constant. So the less air you have, the less fuel you need. You get less power or thrust but that is more than offset by the reduction in drag because of the thin air. At max power our engines on the Gulfstream, for instance, produce a little less than 12,000 lbs of thrust at sea level but at forty five thousand feet we only get a little less than 4,000 lbs. But at forty five thousand feet, the fuel flow is not a whole lot more at cruise power than what we see on the ground at idle. So we try to get up and stay up as long as possible. This includes climbing as we burn off fuel and our lighter weight let's us get up even more. Landing takes total concentration no matter what the weather. Many will tell you it's just a walk in the park but those guys are accidents waiting to happen. We have what we call the "sterile cockpit" rule anytime we're below 10,000 feet. No conversation is allowed in the cockpit that is not relevant to flying the airplane. That includes the boss's pretty daughter sitting on the jumpseat watching. We call the airspace below ten thousand "indian country" because it's filled with Cherokees, Comanches, Apaches, Senecas, etc.
4. When an airliner takes off, it has to reach approximately 130-150 mph to achieve lift. It uses almost full power to get to this speed and burns a huge amount of it's fuel (compared to normal cruising flight). If an airliner sat at 1000ft it would have to carry 10 times as much fuel to do the same journey. The main reason an airliner flies at a certain altitude (30-40,000ft) is to make use of the 'jet-stream'. The jet-stream is a very fast moving (>60mph) stream of air in the middle atmosphere that will carry the aircraft far faster (and therefore more efficiently) than it could ever achieve under it's own engine power and fuel capacity. Imagine walking at normal speed on a pavement and then getting on a travelator and walking at the same speed. Your walking speed (and therefore effort level) is still the same but your GROUND speed is your walking speed PLUS the speed of the travelator. A plane experiences the same thing when it uses the jet stream to boost it's own progress but with no extra fuel consumption. The jet stream was discovered by accident by bomber pilots who kept missing their targets because their instruments were telling them they were flying at normal speed, but the jet stream was actually carrying them at almost double their top speed. I would hope a 777 pilot would be concentrating very hard on ALL landings but especially ones in bad weather. Any driver or pilot who gets complacent about their control skills is a hazard to himself.
5. The passengers are on a trip, getting high is part of it.
6. I was planning a flight from the west coast to the midwest a couple weeks ago for our airline. Due to part of the pressurization system being inoperative I planned it at 25,000 feet instead of 35,000 feet. That caused about 2,000 lbs more fuel burn for 2.5 to 3 hours of flight time, and this is on a 50 seat regional jet. That's literally a TON of fuel for only 10,000 feet difference in altitude! Imagine the difference on a 777 or 747! I sometimes plan at 37,000 feet because on a 3 hour flight it's not uncommon to save 200-400 lbs of fuel. Jet fuel is approximately 6.7 lbs per gallon so do the math and you can see that adding up my company's 1500 flights per day this can be huge. As for landing, it depends on what weather is going on. Every landing is concentrated upon because anything can happen at any time. Landing in low visibility isn't too bad, it's usually a smooth approach and one pilot is looking for the runway lights while the other is watching all the instruments. The hard approaches are in or near thunderstorms or windshear because control of the aircraft poses more of a challenge and planning the path to the alternate airport, should it be needed in even of a go around, is as important as the approach itself.
7. first fuel efficiency, but also above 18000 is class A restricted Mid air collisions are rare because the sky is big and controllers keep the planes well seperated.
8. Jets are best flown at high altitudes. As we go higher, the density of air reduces. Consequently, the ratio of oxygen present in say one cubic meter of air would be far less as compared to mean sea level where the density is much higher. We, therefore, presume that to burn a certain amount of fuel a certain amount of oxygen must be present. The FCUs (Fuel Control Units) in modern jets are programmed to automatically 'dose' the fuel which is required for a certain density of air, in that they will cater for the percentage of oxygen while releasing the fuel for an 'ideal' clean combustion. At higher altitudes, since the density of air is less, the friction is proportionately reduced. In simple words, the aircraft would move comparatively with less effort from the engines. Less effort from the engines combined with reduced fuel requirements (as explained before) would result in a more efficient flight, with a higher ground speed and lesser fuel consumption. At 1000 feet the fuel efficiency would be horrendous. High air density requiring more fuel, with less ground speed would make flying economically unviable. Pilots landing in really bad weather need total concentration whether flying 777s or any other aircraft. The 2nd nature merely provides confidence and lack of panic under adverse weather or other flight conditions.
9. 1. It's more fuel-efficient. 2. Less air density means less drag 3. Higher true-airspeed 4. Most weather stays at lower altitude 5. Better view!!
10. 1)They actually save fuel at higher altitudes because the air is thinner and they go faster (ground speed). 2)There is also nothing to collide with and keeps the congestion down. It would be very dangerous at 1000 feet. 3)They can fly above the weather. 4)Smoother ride, less turbulance.