Boeing 767 Max speed at sea level?

[superrrnova]

How fast do you think a Boeing 767 could go at sea level? The max operating speed at 1000 feet is 360 knots, but I'm aware if can exceed that speed, just not sure by how much. Is it likely you could make it reach 500 knots? I've done some research on this and I seem to get conflicting answer, some say it would be difficult for the structure of the plane to withstand that speed, others say the engines are incapable of creating enough thrust.

I'm in a discussion at the moment about this, I'm not 100% on how far you can exceed the maximum operating speed, your input would be most appreciated. I'm not planning on doing this by the way. I will explain why if you're interested.

[skwinty]

Depends on what altitude the dive commenced.

;) conspiracy theories ---------------------------->

[Shytehawk]

This has got to be about the silliest question ever on here.

[sycamore]

The limitation on airspeed will generally be for structural and fatigue design limits.Not only that,there would be no genuine reason for the aircraft to be required to go beyond that speed.The only people who are reasonably able to exceed that limit would be the Manufacturers test pilots(usually +10 %) and the certification testpilots(+5 %).The aircraft engines are probably quite capable of having sufficient thrust,but that would depend on weight,temperature ,etc.Also at that structural design point the aircraft is only expected to perform gentle manoeuvres only.However if you were to climb to 36000ft and try to get 360 kts ,you would be at about M1.1;Again ,probably well outside the Mach limit for the aircraft,which I would suspect is appx M.95,again a Manufacturers limit...

[superrrnova]

Firstly I'd like to thank you for your response. Some of you are obviously aware of what I'm talking about which is good. That's the main reason I didn't mention it as I was trying to get a professional opinion without the "he's a conspiracy theorist" response. I'd like to point out that I'm not here trying to back up a theory that I hold, I did see some of the pilots for 911 truth shows after a recommendation from a friend, I also found it extremely interesting. After doing research I found so many conflicting opinions so I wanted to ask people who know what they're talking about without all of the hearsay. I hope you don't mind my curiosity and that it doesn't offend anybody. I saw a few forums and this looked the most professional.

Sycamore, thank you so much for taking the time to address the question I posed, even if it was put forward in a rather lame fashion. Flight 77 was clocked doing 500 knots at ground level, at level flight. The general impression I got touched upon a point made by yourself, these were the details I found most interesting. Basically 500 knots at ground level (1000ft) would have an equivalent airspeed of over mach at high altitude. The FDR data was interesting for flight 77, but I didn't delve into that in too much detail. I was more interested in the capabilities of the Boeing that was supposedly used on that horrible day.

I'm sorry if this topic offends anybody and I'm not a whack job. I don't pay too much attention to the "conspiracy theories" but this was something I didn't want to turn a blind eye too. Thanks for your replies, I look forward to more.

Silberfuchs

I believe the radar data should be fairly accurate, right? :/ Also, flight 77's information was taken from the FDR. The two from the towers apparently weren't as indestructible as they'd make you believe.

[Crazy Voyager]

superrnova, I'm not sure how much experience you have with aircraft and more specifically the topic of measuring speed but you should be aware several diffrent numbers could all be correct.

Now if you know the difference between IAS, TAS, GS etc then you can just ignore this post from here on :ok:

I should say that I study this because I'm trying to become an ATCO, not a pilot, so a lot of people in here do know a LOT more on this than I. How ever I'm sure they will step in to clarify or correct me should I mess up somewhere.


The radar data will show a Ground Speed (it's based on the difference in position between two radar updates and calculated using that and the time lapsed). It gives you a number showing how far the aircraft travelled over the ground at that time.

The aircraft's instruments will show Indicated Airspeed (IAS). It shows the speed of which the aircraft moves through the air. The IAS varies with many things (such as winds for example). This means that it's many times not equal to the GS (shown on radar), at high levels the IAS and GS can differ by more than 100 knots.


I belive the FDR shows IAS (because it's a reading of the instruments) and the radars will show GS, so you might see different values here and you must also be aware about this difference when looking at speed limitations specified by the manufacturers.

[Shytehawk]

Crazy Voyager

I think that you will find that you are mixing up the relationship between IAS and TAS ( True Airspeed ) with the relationship between IAS and GS.

IAS when corrected for temperature and pressure gives you TAS.
TAS when corrected for wind vetors gives you GS.

Good luck with your application.

[Northbeach]

How fast do you think a Boeing 767 could go at sea level? The max operating speed at 1000 feet is 360 knots

Do you realize that for all practical purposes there is no difference between sea level and 1,000' above sea level, or even, 2,000 above sea level for your question?

If the aircraft limitation is 360 knots of indicated air speed at sea level, it will have the same limitation of 360 knots indicated air speed at 1,000' and 2,000' above sea level.

This "limitation" is what the manufacturer says is the fastest speed the airplane should be flown. It does not, in any way mean, it is the fastest airspeed the airplane is capable of flying. I am not a test pilot, therefore I do not fly my jets faster than the manufacturer, airline or regulating authority tells me to fly the jet. So I do not have any (......well much) practical experience beyond the barber pole/red line.

Let's shift this discussion to the more familiar automobile world for a moment. The posted speed for the road is the maximum allowable on the autobahn/highway/freeway it does not in any way mean that the automobile you are driving is incapable of driving at speeds in excess of the posted limit. I assure you that your Porsche, Mercedes, humble Fiat or Chevy and many other types are capable of speeds in excess of what is legal on the public transportation grid. To confuse the two and believe that the machine is incapable of exceeding an external posted limit (or a printed speed limit in the limitation section of the flight handbook) is to be extremely ignorant of the subject matter.

If you take the power levers and shove them full forward at or near sea level (up to 2,000' for this discussion) your 767/757 will in fact fly at a greater speed than 360 knots indicated airspeed in level flight and/or descent. It will keep accelerating until total drag equals total thrust or until something fails structurally and the jet comes apart (or runs into something solid). Each individual airplane will likely fail at a different speed as they each wear and fatigue differently over their operational lives. Could the 767/757 reach > 500 knots under the stated conditions I'd be comfortable betting a month's wages on "yes".

[superrrnova]

Thanks again for your replies all. As I said, I'm not here trying to get under your skin. I'm just sick of hearing "this pilot thinks ....". That's why I have asked the question here.

North: "Do you realize that for all practical purposes there is no difference between sea level and 1,000' above sea level, or even, 2,000 above sea level for your question?"

Yes sir, sorry I didn't mean for that to sound so important. I just meant a low altitude in comparison to cruising altitude. I didn't need the car analogy. I have a grasp of what the maximum operating speed means, that speed which is safe to operate within. The question was more about the physical barriers hindering that speed at low altitude. Someone used a "moving your hand through water as opposed to through air" analogy to explain in a term easy enough for my little brain to describe what it would be like. I understand what you're saying though, I think they may have over-emphasized the drag effects at low altitude. Being as you'd bet a months wages I will take on board what you have said for sure though, North. Thank you for taking the time to explain a few area's that I'm unfamiliar with. I appreciate it

[Northbeach]

I have a grasp of what the maximum operating speed means, that speed which is safe to operate within.

And here is why. When the aircraft encounters turbulence the G-loading (force of gravity) can change in a very short amount of time in several different load directions (pitch, roll and yaw). If the wings are supporting 100 tons of jet in level unaccelerated flight and then encounter turbulence, the loads carried by the wings, attach points and all of the other supporting structures can virtually instantaneously experience an increase of 30%-40%-50% or more in one direction followed by a change in the opposite, or combination (twisting) direction. It's very hard on equipment; all of this happening at close to the speed of sound. With a minor change in temperature one can find themself immediately at a higher airspeed magnifying the overload condition.

It is for this reason that manufacturers are required to build aircraft much stronger than the minimum acceptable levels under normal operation. And the jets need to last a long time; think decades.

The written airspeed, weight, loading limitations are much lower than what the aircraft could actually perform at-under ideal conditions. This provides the safety margin that is so important for all of us.

Look up the Boeing 787 wing stress test on Youtube. The wings are subjected to extreme overstress conditions, far beyond what the crews are allowed to operate in, before they actually fail. There is a large margin between the "written" limitations and the actual physical limits of the 757/767-pick your jet.

For somebody (not you) to say that the 767 limiting airspeed at sea level is 360 knots, therefore the jet is not capable of flying any faster at sea level or 1,000' would be an incorrect statement.

[Crazy Voyager]

@shytehawk
Looks like I need to go back to my books and study :8