The bigger jet airliners need to approach and land substantially faster than 100 mph. A Boeing 737 (like all of Southwest Airlines planes) for example is on the smaller end of these and will still need to land at 150 mph or faster and approach even faster than that. A 747 might need to touchdown at 175 mph. Exact numbers on these are impossible because it depends on landing weight and the wind among other things but those are some good ballparks.
Regional jets may be able to land around the 100 mph mark and smaller piston plane can land lower than that. In other words, it depends on the type and class of the plane but the big ones just can’t fly that slow.
Thanks Shagnasty. So a string of 747’s that are 5 miles apart would land every 1.7 minutes. That’s very close to King Friday’s observation. Of course, it a rough calculation since the planes are decelerating during those 5 miles. Do planes accelerate right before the touch down or does it just feel that way?
No acceleration at the end. The deceleration should all be done by 1000 feet above the ground, and from there until touchdown a constant speed is maintained. You usually slow down a few knots just before the wheels touch the ground, but it’s minor (3 or 4 knots) and nothing that can be felt. If you are sitting near the engines you might notice the power settings change while on short final. This is most noticeable in gusty wind conditions. As the airplane flies through various wind gusts the power is changed to maintain the same airspeed. In some cases the headwind might drop off at the last minute and the power will be advanced rapidly, but again the goal is to maintain the same airspeed, not accelerate.
One word on landing speeds - for commercial jets the biggest variable is the weight of the airplane. The approach speed of a 737 might vary by 20 knots depending on how heavy the airplane is. Most commercial airliners landing at normal weights will have an approach speed of around 120-130 knots. Manufacturers design all kinds of complicated flap and slat systems on wings that allow them to slow down the landing speeds. A higher landing speed means MUCH more runway required for landing, and manufacturers want their airplanes to be as versatile as possible.
No. The spacing requirement is in time, not distance. A 3-minute spacing between 2 planes landing at 60 knots is half the distance of the 3-minute spacing behind 2 planes landing at 120 knots.
Not in all cases. Like I said up thread, small plans can be landed on the same runway at the same time as long as they are never closer than 3000’ to to each other.
In practical terms, the first plane can have missed the middle turn off of a long runway and be taxing down to say the end one and if he is say 4000’ feet from the approach end, the tower can ask the next plane if he can land in the first 500’. An affirmative reply will get him landing clearance to do so along with a warning about the other aircraft on the runway.
If he fails to get down in time he will be told to go around and he will lose his place in line. They will also remember him and he may not get other chances from that controller to do the same thing other times.
There are a lot of things that the controllers can let you do according to the letter of the law but safety is first. If you can’t ‘hack it’, you will get the maximum safety way regardless of wither it is convenient for you.
Do not piss off the controllers without a real good reason, you life will be much more pleasant.
Big Iron generally do not do this although they can cut it pretty fine when one is at the far end of a 10,000’ runway.
The planes and pilots are entirely capable of landing closer together but they are so big, fast and heavy with much momentum that it is much better to err on the side of caution and try to prevent even a one in a million chance when it is so easy to do so.