Can airplanes easily go top speed close to the ground?

[spooked911]

I am wondering in particular about planes like flight 93 and flight 77 that were supposedly going 500-580 mph very close to the ground. How easy is it to control a plane going that fast close to the ground? Are there ground effects that could make piloting the plane at that speed even harder?

Also, the 9/11 commission report refers to the pilot of flight 77 pulling back the throttle all the way before he crashed into the Pentagon. If you suddenly accelerated, wouldn't this tend to cause the plane to lift up? However flight 77 supposedly made an incredible level descent into the first floor of the Pentagon. This seems very improbable to me.

Any pilots here or anyone who knows about this stuff?

[demodewd]

1. air thickness

I'm not a pilot but it is my understanding that the air is thicker at near ground levels prohibiting airliners to reach the speeds they can reach at lets say 30,000 feet.

[spooked911]

3. that was my understanding as well... but I didn't know how important

it is for sub-sonic speeds.

[DrDebug]

2. I am not a pilot, but there must the vacuum effect

If you go incredibly fast then you create an enormous vacuum behind you which you gives you a lift upwards. For example race cars have an inverted wing to prevent the car from taking off ( http://people.bath.ac.uk/ip206/Aerodynamic%20in%20car%20design/General%20Principles%20of%20Aerodynamics.htm )

So you need to pull the airplane down, but that's the problem with flying that low. The point is really the speed, if you go "slow" then you could very well keep the plane flying at a low altitude, but at speeds like 500mph.

The take off speed for the 757-200 is 140-145kts (~165mph) which is at least THREE times slower then the above mentioned speed. ( http://www.jersey-va.co.uk/Aircraft-specs/boeing_757.htm ) This website also mentions Vat 137-140 knots Landing @ Runway Threshold Speed @ MLW full flap/Gear down and if that is the Threshold then there is bound to be a Electronic Speed Limit set up somewhere or at least some flashing lights if you exceed it by too much. It also says:

* DO NOT Exceed 250kts @ or Below 10,000ft Altitude. *

And the altitude was what 10 ft??

Edit: DO NOT Exceed added

[spooked911]

4. great links!

I like how this was set alone in red:

"* DO NOT Exceed 250kts @ or Below 10,000ft Altitude. *"


It sounds like that might be important. Probably because you could easily lose control or have the plane start to break up.

So the question is how improbable does this make the official flight 77 into the Pentagon story?

It already seemed improbable to me, but is this another nail in the coffin?

[DrDebug]

5. It must be important

But I guess we need a pilot to tell us why it is important. It means that you can go faster then ~280mph but you really shouldn't try it.

There was a story about that blurry security camera with a calculation which gave a ridiculous speed (10 times the speed of sound or something like that). So the speed of the object would definitely be higher then a "mere" 280mph thus exceeding a specific warning for this kind of airplane.

So the question is how improbable does this make the official flight 77 into the Pentagon story?
We know that the speed was incredibly high. Reports of 400mph and more. So it would have travelled at at least 350mph at the time of impact if not much more. It makes it more improbable, but we need somebody to explain the red stuff on the site.

[RedSock]

6. the WTC planes

Both WTC planes were "officially" going more than 500 mph, weren't they?

They must have been below 10K for quite awhile also.

[DrDebug]

7. Yes, both were flying at almost the double speed

They were flying at about 300m (1000 ft) at the point of impact.
http://web.mit.edu/civenv/wtc/PDFfiles/Chapter%20III%20Aircraft%20speed.pdf

WTC1: approx. 410 knots, or 470 mph
WTC2: approx. 510 knots, or 590 mph

http://911research.wtc7.net/mirrors/guardian/WTC/WTC_ch1.htm

And the 767 (or the 737 drone) both had the same limitation on the other website

[FloridaPat]

10. That is the federal law. No one can legally fly above 250 knots

10,000 and below. Has nothing to do with aircraft control.

[spooked911]

21. That makes sense, thanks.

[Old and In the Way]

8. If the plane is going 500 MPH.......

how does anyone see tail markings, windows, etc. All the eyewitness reports seem to be saying a plane approaching as if it was landing with it's gear up. You don't see those details if the plane is flying 500 MPH?

Anyway, I don't know how Hans Hanjour executes a 270 degree, 7000 foot drop in such a tight radius at cruising speed without destroying the airframe. He needs to control the throttle, airbrakes, wingflaps, rudder in a very defined and controled manner. He gets one shot to do it and he doesn't destroy the airframe in the process? This from a guy who, we are told, doesn't belong in a Cessna, let alone a 757?

Let's do the math-

500MPH is 8.33 miles/minute (say 44,000 feet). It covers 740 ft a second. Would it even register on people's brains before it hits the Pentagon?

[spooked911]

9. No, I don't think it would register. I think they just saw something

flying really fast and thought it was an airplane. I think it was a missile.

[FloridaPat]

12. Military pilots do this all the time with military approaches.

They drop straight down from around 10,000 to the runway in a tight circle. That would be the class of pilot of board. As for the airframe, those planes are very well built. A B727 did several rolls at around 35,000 feet several years ago. No one could figure why. Injuured quite a few people. They the airlines started laying people off and the co-pilot tried to make a deal - he keeps his job and he tells them what really happened. The cause of the accident was the captain disconnected the fuse to the controls that keep the aircraft below mach 1. The captain then pushed it near mach one to try to make up some time. The navigator came back into the cabin, saw the fuse and pushed it in. The aircraft immediately tried to slow down and in the process did some very nice rolls.

And as for the details - if you look at the film of the planes running into the WTC, you will notice the landing gear is down.

[Old and In the Way]

13. I agree.

But could Hans Hanjour do that in a 767? I'm sure the roll was stressful, but an experienced pilot could probably handle it.

I don't recall seeing any landing gear down on 175....I have no idea about 11, because I've never seen clear pics of the aircraft.

[FloridaPat]

14. Those planes can do a lot. They usually don't do fancy things because

pulling passengers off the ceiling is not good company policy. However, the jets were filled to the gills with gas, people and luggage. I don't recall that plane doing much over Washington because the original report said it was looking for the White House, couldn't find it so it went for the pentagon. I will have to look at the reports again.

As for not finding the White House - I flew out of DC last year. One would have to be blind to not find the White House.

[Old and In the Way]

18. What was the hurry?

77 flies out to Ohio and back and can't take an extra loop around DC to line up the WH? It's not like they had AF interceptors on their tail. I assume the terrorists studied a map of Washington. Hell, if they can fly a 757 like an F-16, how hard would it have been to locate the WH? Based on the alledged flightpath, he should have gone left, instead of right..

[FloridaPat]

24. The government did come out a few weeks later and said they were

"mistaken" about the plane looking like it was looking for the White House. They just wanted everyone to feel sorry for the idiots in the White House. This was one of two items I paid particular attention to because it sounded a little strange. And it turned out it was. The government started lying from day 1.

[spooked911]

20. Perhaps you could point me to which film it is that shows that?

I've seen a lot of different videos and pictures of the jets hitting the WTC but never seen the landing gear down.

[FloridaPat]

11. Air force and navy jets go that fast near the ground all the time.

It just happens to be a federal law that planes can't fly that fast below 10,000. The military jets have special areas that are closed to everyone else where they plan their war games and fly at very high speeds.

The plane that flew into the pentagon had some very fancy piloting done. Two things that effect a plane near the ground is wind shear and sudden rising from heat of the land. There was no wind shear apparently that day. Although I think at 500 knots the plane may not be effected by much of anything. The pilot did a perfect landing without hitting once blade of grass. That is impressive.

Other facts: a large jet takes about 3 minutes to respond to the controls. Hard to imagine people taking a few rides in a cessna and then doing simulators to do what was done on 9-11. Now if the WTC had some kind of navigation signal, I can see them doing what they did. That was very sharp flying.

As for how fast one can fly, the speed of sound varies on temperature. Mach 1 is faster at 30,000 feet than at 1000 feet.

My background is a little flying and 9 years as an air traffic controller. Yes, every time the repubs are in office I have to get a new career.

[k-robjoe]

16. question

> "a large jet takes about 3 minutes to respond to the controls."

I don´t get what is meant, it can´t possibly be that it takes three minutes from the time you turn left, until the plane actually turns left. ( Did you mean to say "seconds"? )

[FloridaPat]

17. It's beena long time. It takes about 20-30 seconds for the response.

Yes, minutes is too long. So for these pilots to aim at the WTC and be flying at the speeds they were, and to actually hit them as well as they did plus do the little banking manuver they did right before the crashed into the buildings - these were no cessna pilots. I'd believe remote controls and some sort of navigation beacon before I'd believe cessna pilots did this.

[spooked911]

19. Thank you-- that is really interesting.

[Sweet Pea]

22. Just a couple of comments.....

It just happens to be a federal law that planes can't fly that fast below 10,000. The military jets have special areas that are closed to everyone else where they plan their war games and fly at very high speeds.

Very true. The practical limitations on aircraft flying that fast are structural limitations that are unique to the aircraft. Panels start to open up, the hydraulic pressure that keeps things like landing gear doors closed are overcome by the air pressure. The 250 knots below 10,000 feet rule is indeed a hard and fast one enforced by the FAA and that has more to do with noise abatement and sequencing of aircraft in the low altitue structure than anything else. Many, many more things are flying around below 10,000 feet and having someone/something zorching aroung at 400 or 500 knots leaves precious little time for hazard calls and/or aircraft avoidance manuevers.

Other facts: a large jet takes about 3 minutes to respond to the controls. Hard to imagine people taking a few rides in a cessna and then doing simulators to do what was done on 9-11. Now if the WTC had some kind of navigation signal, I can see them doing what they did. That was very sharp flying.

I have no idea where you came up with this tidbit - minutes or even seconds. Modern jetliners have digital fly-by-wire controls. Any control input is instantaneously transmitted to the control surfaces (flaps, ailerons, rudder, spoilers, etc) and then act upon the aircraft flight characteristics immediately. Even the older airliner flight controls are hydraulically boosted and the inputs to flight controls are virtually instantaneous. True, high speed (and by association heavy airflow over the aircraft surfaces) affects the ability of a control surface to defelct into the airflow (Chuck Yeager spoke about this in his autobio, but he also had supersonic air compression deals going on with an experimental aircraft in a flight dynamic that had never been experienced before), but the speeds these airliners were flying would not have proved difficult for control inputs to be made and the aircraft response would have remained immediate.

As for how fast one can fly, the speed of sound varies on temperature. Mach 1 is faster at 30,000 feet than at 1000 feet.

Backwards. The dense air in lower altitudes means the aircraft has to fly faster to achieve mach. Thin air at higher altiudes means the aircraft reaches mach at a lower airspeed.

The speed of sound (or "mach 1") depends on more things than just temperature...air density, humidity, wind speed just to name a few.

"At sea level, the speed of sound is about 761 miles per hour (1,225 kilometers per hour). At 20,000 feet (6,096 meters), the speed of sound is 660 miles per hour (1,062 kilometers per hour)."

http://www.centennialofflight.gov/essay/Dictionary/sound_barrier/DI94.htm

[FloridaPat]

23. Where I got the 20-30 second response time:

I told a pilot of a large aircraft he was cleared for an immediate takeoff. When he seemed to be taking his time, I reitereated the immediate part with a much higher pitch to my voice. That was when I got a lecture on hydraulics and response time of jet aircraft.

About the speed of sound - if it's -30 degrees at 20,000 would it still be 660 miles per hour? There doesn't seem to be that much between the two altitudes with your numbers, so I wonder why it took so long to crash the speed of sound and why it had to be so high in the sky? Just curious. I don't think I've seen aircraft below 20,000 feet go near mach 1. It's usually for the higher altitudes.

[MercutioATC]

25. And I swore to myself that I was going to stay out of the 9/11 Forum.....

geez....


Your reply to #1 is total B.S. and shows a complete lack of understanding of aviation.

"The practical limitations on aircraft flying that fast are structural limitations that are unique to the aircraft. Panels start to open up, the hydraulic pressure that keeps things like landing gear doors closed are overcome by the air pressure."

Any plane certified to fly above 250k can do so at 11,000' or 9,000'. It makes absolutely no difference. 10,000' is not some magic altitude at which "panels start to open up".


"The 250 knots below 10,000 feet rule is indeed a hard and fast one enforced by the FAA and that has more to do with noise abatement and sequencing of aircraft in the low altitue structure than anything else."

Again, B.S.
It has very little to do with either noise abatement or sequencing (it actually makes sequencing more difficult). It has everything to do with preventing jets from eating slow-moving VFR props.

The only thing you stated that makes any sense is "Many, many more things are flying around below 10,000 feet and having someone/something zorching aroung at 400 or 500 knots leaves precious little time for hazard calls and/or aircraft avoidance manuevers."

THAT'S the real reason for the rule...


...and, by the way, it's not "a hard and fast one enforced by the FAA". Ask any ATC or honest pilot and they'll tell you:

1) there's no way the FAA CAN enforce it, and

2) because of that, it's broken on at least an occasional basis.



I really hate the fact that I felt compelled to reply to this...but there was just too much bullshit being slung for me to ignore.

[Sweet Pea]

27. OUCH!

Spanked by the ATC!

I used my words poorly.

"The practical limitations..." comment was indeed address towards why aircraft have speed limitations at specific altitudes and shouldn't have been aligned with the FAA 250 knt rule below 10k. For example, the F-14 program was issued these restrictions in 1996 for a period of time based on aircraft engine problems:

The following requirements and limitations are intended to
permit safe operation of the F-14 aircraft pending completion of
the investigations:
-- F-14A and B aircraft will fly at less than 550 knots when
below 10,000 feet altitude.
-- F-14B aircraft will have use of afterburners restricted
when below 10,000 feet altitude.
-- F-14D aircraft will fly at less than 550 knots when below
10,000 feet altitude (below 17,000 feet if Phoenix fairings are
installed) and will also have restricted afterburner use when
below 10,000 feet altitude.

http://www.chinfo.navy.mil/navpalib/news/navywire/nwsa96/nwsa0227.txt

Again, my bust for equating this with the FAA restriction of speed and altitude.

The noise abatement and sequencing comment was based on my experience flying in and around military bases for most of the 10 yr period from 1985 to 1995. Base course rules were specific with regards to flying in and around the field TCA (terminal control area) and if one busted them it was likely the pilot became the instructor for the Base Course Rules lecture. In addition, most of these military airfields, over time, have ended up in the middle of extremely populated residential areas and as such the course rules were written with that at least partially in mind.

With regards to enforcement of the 250 kt/10K rule, only speaking for myself, FAR 91 regs were pretty much the rule, at least for the years I flew, and we strove to adhere by those regulations:

Sec. 91.117 Aircraft speed.

(a) Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).
(b) Unless otherwise authorized or required by ATC, no person may
operate an aircraft at or below 2,500 feet above the surface within 4
nautical miles of the primary airport of a Class C or Class D airspace
area at an indicated airspeed of more than 200 knots (230 mph.). This
paragraph (b) does not apply to any operations within a Class B airspace area. Such operations shall comply with paragraph (a) of this section.
(c) No person may operate an aircraft in the airspace underlying a
Class B airspace area designated for an airport or in a VFR corridor
designated through such a Class B airspace area, at an indicated
airspeed of more than 200 knots (230 mph).
(d) If the minimum safe airspeed for any particular operation is
greater than the maximum speed prescribed in this section, the aircraft may be operated at that minimum speed.

http://www.gofir.com/fars/part91/index.htm

We flew one F-14 from Calverton, LI to Miramar, CA entirely in the low-altitude structure once - tacan to tacan (vice via jetways or INS direct) or even cancelling and proceeding VFR when we could. Was one of the more enjoyable days I ever spent flying, and I'd say 98% of it was at 250kts or below - not only because we could do it at that speed but because that was the rule (re: the other 2% - we asked for and received clearance to speed up some for weather or other requirements at times.)

1) there's no way the FAA CAN enforce it, and

2) because of that, it's broken on at least an occasional basis.

I'm a bit surprised that the FAA would take such a cavalier attitute towards this. It was my experience that simply because it was a FAR regulation that it was meant to be adhered to. I would submit that it can be enforced if desired but aircraft and controllers (MY OPINION) likely don't ALL THE TIME because of a "no harm no foul" attitude, as long as it is not abused. Heck...I've been mach 1.2 at 50 feet, but that was in a MOA near Fallon, NV. I've also been anywhere from 260 kts to 350 kts or faster while approaching the field for the overhead break, but that was in the approach/landing environment in a Navy field TCA.

The aforementioned post is a compilation of my own thoughts, opinions, observations and published, established procedures and standards.

Anyhow, apologies for my poorly worded post and I'll strive for better lexicon usage and arrangement in the future.

And I *do* have a fairly good understanding of aviation, thankyewverymuch - so there! :)

[DoYouEverWonder]

26. The part that I don't get

is who in the world, with that kind of training and experience, to maneuver a jumbo jet with such skill, would be willing to suicide themselves? No less, at least 4 with pilot training? One more piece of this puzzle that doesn't make sense.

[LARED]

15. supposedly going 500-580 mph

Does anyone actually know if an estimate was made of the speed?

The 9/11 report makes mention of the actual speed of eother plane. I have found no credible information anywhere.