Max Test flight Mach Number for the 737NG!

[Jetpipe.]

Good evening people!

While watching this video I got curious to know what was the 737NG's max Mach number it was able to reach during its test flights.

https://www.youtube.com/watch?v=s3-g9B6Fgjs

Anybody know? Do you have info about other airliners?

[G0ULI]

This was discussed at some length on this very site ten years ago. I believe the consensus arrived at was 0.02 mach above maximum operating speed.

[KayPam]

Well that was wrong.

Each and every airliner (and airplane) has been tested up to VD/MD.
VD/MD are velocity dive and mach dive. They are defined in the certification standards, as the speed the airplane would reach if it started to dive (with a specific diving rate) with cruise power.

Some examples :

A320 MMO 0.82 MD 0.89
A330 MMO 0.86 MD 0.93
A380 MMO 0.89 MD 0.96

There are values for these speeds in knots as well, but not presented here.

Actually, an A320 can fly easily at M0.84-0.85, it still won't be very dangerous.

Some airlines will conduct their own "test flights" and test some features of the flight control laws.
Here is how someone can know if a speed is acceptable.
The greater the speed, the more the flight control law will pitch up the aircraft (with neutral sidestick). At M0.84, the pitch up is very slight. It will become much stronger at M0.86 or something.

One source :
?Diving? into the A320: Dive Speeds | The Flying Engineer (http://theflyingengineer.com/2012/03/18/diving-into-the-a320-dive-speeds/)

[tdracer]

During the flight testing of the 747-8, I personally looked at flight test data between Mach 0.98 and 0.99.


No idea how hard they pushed the Max.

[safelife]

I always believed the required margin was 0.07 mach, at least you'll find that most aircraft nowadays have been tested that fast.

[KayPam]

Tdracer : i would have liked to say the 380 was tested up to 0.99 as well but could not confirm that.

Well, one more reason why Bonin and Robert should have pushed on their stick : they did not risk anything

[FCeng84]

The margin between maximum operating speed (Vmo or Mmo) and dive speed (Vd or Md) is defined in the regulations involving a dive condition without pilot intervention for a number of seconds. Airplanes with overspeed protection functions in their control laws have been able to certify with less operating to dive envelope margin.

[vilas]

KayPam


Aircraft type VD Kts
A350 375
A380 375
A330/340 365
A320 Family 381

Actually, an A320 can fly easily at M0.84-0.85, it still won't be very dangerous

How do you reconcile this statement with Airbus which says:


Crews should keep in mind that
•At high altitude, whilst it is important to always respect MMO, a slight and temporaryMach increase above that value will not lead the aircraft into an immediate hazardoussituation. At lower altitudes, exceeding VMO by a significant amount is a real threatand can dramatically affect the integrity of the aircraft’s structure.
Althoughintentional VMO/MMO exceedance cases are rare, this limit speed can typicallybe overshot when the aircraft is subject to unusual wind and/or temperaturegradient. Prevention is therefore essential.
VMO/MMO IN A NUTSHELL
VMO/MMO is the “never TO exceed” speed

[cosmo kramer]

Easyjet flew a 737NG at 447 kts by accident. No damage was found to the aircraft. I'm sure you can dig up the investigation report on google.
*Edit, there you go: https://assets.publishing.service.gov.uk/media/5422f73640f0b613420005db/Boeing_737-73V__G-EZJK_09-10.pdf


Personally, I have once flow 0.86 during a severe shift of 100 knots cruise winds. With thrust at idle and speed brakes extended the speed just kept going up. Otherwise, it was completely uneventful.

These things are built like tanks.

[westhawk]

These things are built like tanks. Be that as it may, Vmo and Mmo are established according to Vdf and Mdf. The maximum demonstrated dive speed is the highest speed at which certain problems are not encountered in during the certification flight test series. See AC25-7C (http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2025-7C%20.pdf) section 8 for more detailed flight test procedures.

Exceeding the published Vmo or Mmo by a small amount eats into the rather small margin between the published operational limit and the flight test demonstrated limit. The flight test demonstrated dive speed was established on a new airplane by the way. There's really no guarantee that aeroelastic or structural limits won't be reached at less than Vd or at a lesser load factor than was found acceptable during testing. Since a line pilot has no way of knowing which test conditions may have been found to be speed limiting during flight tests, there is no way to know which deleterious effect will be encountered first above the limiting speed.

While a number of older part 25 jets have flown well beyond established airspeed limits during certain incidents occurring in line service, many of these resulted in serious damage or control difficulties. Or sometimes much worse.

Nor would I count on newer airplanes to be built with the same level of "over engineering" as older types either. So all things considered, I wouldn't prefer to deliberately exceed published Vmo/Mmo unless it were somehow a better option than the available alternatives. In all likelihood it'll stay together and remain controllable up to the speed the test pilots took it to. Why would I want to take the airplane out into a flight regime the test pilots didn't?

At some point most jet pilots will inadvertently exceed Mmo when encountering certain unforeseen atmospheric conditions. Most commonly during descent into colder air or increasing headwind component. Because a margin of between .05 to .07M exists Between Mmo and Mdf, no structural damage or loss of controllability should occur during a minor exceedence. In some types this may be getting very close to real trouble. Others may provide a more generous margin than strictly required. A number of aircraft have been lost during flight test while exploring the corners of the speed envelope.

Until some some kind soul offers to pay my way through test pilot school, I'll just stick to the limits established by the trained and qualified test pilots who conducted the certification tests. Why do otherwise?

[vilas]

These things are built like tanks.
I am not so sure. Most accident where 737NG has left the runway the fuselage has broken up.

[Valmont]

Vilas, from the Airbus Safety First #21 (http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presentations/2016/Airbus%20Safety%20First%20Mag%20-%20January%202016.pdf)

How is VMO/MMO determined?
VMO/MMO is established with regards to the aircraft’s structural limits and it provides a margin to the design limit speed/Mach number VD/MD. VD/MD must be suf ciently above VMO/MMO to make it highly improbable that VD/ MD will be inadvertently exceeded in commercial operations. Several certi cation criteria exist. As a result, on Airbus aircraft, MD is usually equal to MMO + 0.07 and VD approximately equal to VMO + 35 kt.
The applicable VMO/MMO are indicated in each Aircraft Flight Manual. For example, VMO/MMO and VD/MD are given in the following table.


Given this, I think KayPam might be right.
Page 13 for anyone interested !

[stilton]

vilas,


Big difference between inflight air loads and overloads that an aircraft structure is optimized and designed for vs actual impact to the airframe in an off runway excursion.


Personally I do believe Boeings are built like 'tanks of the air' their strength has been proven time after time in decades of service (in some quite incredible events far outside the certified flight envelope) and i've never seen a paragraph in any Boeing flight manual warning me that structural failure may occur if I exceeded VMO / MMO

[MarkerInbound]

We won't talk about DC-8s.

Ok, we will.

History, Travel, Arts, Science, People, Places | Air & Space Magazine (http://www.airspacemag.com/history-of-flight/i-was-there-when-the-dc-8-went-supersonic-27846699/)

[vilas]

Valmont, stilton
What I quoted is exactly from the same issue of Safety first page 15. I don't know how did you miss what is written in bold letters. There is a difference between occasional speed excursion caused by environmental factors beyond control and deliberately doing it for a sustained period of time. The manufacturer has given you VMO/MMO. They don't have to tell you anything more. If they had your confidence wouldn't they increase the VMO/MMO figures? Commercial aircrafts are not combat aircrafts. Built like tanks is a very non professional lay man like statement. Nobody builds them even a bit more stronger than required because it adds to weight which reduces payload and increase fuel consumption.
Big difference between inflight air loads and overloads that an aircraft structure is optimized and designed for vs actual impact to the airframe in an off runway excursion. Yah, But Sully's airbus didn't brake up despite him dropping speed considerably but 737NG broke up in Bali. You are advised to see the documentary made by Al Jazeera on Boeing especially 737NG.

[FCeng84]

There are many factors that go into designing airplane structure. Two basic issues are strength and fatigue. This is particularly an issue for aluminum wings. For many portions of an aluminum wing fatigue is the designing factor. Those sections must be thick enough to resist developing fatigue cracks and to reduce the growth rate for any small cracks that do form. Given enough material to meet fatigue requirements, that portion of structure may be able to withstand loads associated with speeds well beyond Vd/Md.

An interesting change in design practice has come about with the use of composite materials. Composites have much less tendency to fatigue and thus design with these materials is driven more by maneuver and ultimate gust loads. An important result is that structures can be build with less material and there is design incentive to reduce maneuver loads as that allows for further reduction in the structural gauges. A fallout of all of this is that an older model with primarily aluminum structure may be more tolerant of increased loads associated with exceeding Vd/Md than a newer model built with composite materials.

The bottom line is that airplanes should be operated at/below Vmo/Mmo so that inadvertant exceedences of Vd/Md are highly unlikely.

[KayPam]

Vilas : VD and MD are two different things (obviously).

If you were to fly faster than MD at a low altitude, you would be way past VD, and the impact pressure would damage your aircraft or even destroy it

So yes, you can fly at a high altitude at MMO+0.03 without a problem, that's because the problems caused by a high mach number with a low VD are different than those caused by a high impact pressure.

However, the incident cited in a previous message with a 737 NG at a low altitude reaching 430kt proves that there is still a quite large* margin behind VMO/MMO

*Please don't overinterpret this "quite large". A quite large mach excursion in my mind would be a quarter of the difference between max operating and dive speeds.
Please also do not consider my messages as an encouragement to fly past VMO/MMO :)
Even more so on a regular basis.

I am just saying that you should not panick if your aircraft were to exceed VMAX by a bit.
VMAX includes VFE, which also has a margin before slats/flaps destruction. Slats and flaps should jam before breaking.
In my airclub, a pilot anonymously reported exceeding the VFE by about 15kt on a light aircraft, during a few minutes. The plane was inspected and nothing was found.

This is all thanks to the 50% margin that airplane makers have to guarantee, between the maximum autorized ("legal") load and the load that will actually break the airplane.

[stilton]

It was calculated that the indicated airspeed of one of the 767's that hit
the WTC was over 460 Knots, the old girl stayed together as long as she could..

[CONSO]

During the flight testing of the 747-8, I personally looked at flight test data between Mach 0.98 and 0.99.


No idea how hard they pushed the Max.


perhaps the cockpit hump had an 'area rule' effect ( less drag ) at near supersonic speeds ??

[tdracer]

perhaps the cockpit hump had an 'area rule' effect ( less drag ) at near supersonic speeds ??
It does, and you don't need to be flirting with Mach 1 - it makes somewhere between 0.005 and 0.010 Mach improvement in optimum cruise speed.
Supposedly, when they extended the upper deck for the 747-300/400, the improvement in area rule effectively cancelled the increase in weight of the extra structure.

[vilas]

Actually, an A320 can fly easily at M0.84-0.85, it still won't be very dangerous The wording of your statement is wrong which makes it dangerous. You definitely never do it intentionally but if it happens due to circumstances beyond your control you have to take extra care not to allow that to happen again till you land because sitting inside you cannot assess exactly the extent of damage if any. Airlines do not have test pilots to do this kind of testing. Some airlines will conduct their own "test flights" and test some features of the flight control laws.
Here is how someone can know if a speed is acceptable. No amount of testing will permit you to modify manufacturers speed limits. China airlines B747 did a barrel role and yet everyone survived it doesn't mean it can easily be done.

[westhawk]

China airlines B747 did a barrel role and yet everyone survived it doesn't mean it can easily be done.

If I recall correctly, that airplane was repaired and returned to service. I'm pretty sure it wasn't cheap to repair the extensive structural damage done during the high speed dive and pullout. A 5 gee pull in a 747 is impressive indeed, even if it did cause the loss of nearly half of the HS and elevator surface. Don't try this at home kids!

[vilas]

If I recall correctly, that airplane was repaired and returned to service. I'm pretty sure it wasn't cheap to repair the extensive structural damage done during the high speed dive and pullout. A 5 gee pull in a 747 is impressive indeed, even if it did cause the loss of nearly half of the HS and elevator surface. Don't try this at home kids!It was a write off never flew again. I think it was left at SFO.

[tdracer]

A 5 gee pull in a 747 is impressive indeed, even if it did cause the loss of nearly half of the HS and elevator surface.Most if not all of the damage to the horizontal tail was not due to aerodynamic forces. The landing gear uplocks failed and the gear deployed through the landing gear doors during the pullout - the debris from the gear doors is what damaged the tail.


Vilas, my memory is the same as westhawk - it returned to service. According to Wiki:
After repairs were made to the plane, it returned to service on April 25, 1985. It continued in service for nearly 12 years until it was leased to China Airlines' sister company, Mandarin Airlines (https://en.wikipedia.org/wiki/Mandarin_Airlines), on January 1, 1997, and was in daily service for the remainder of that year.[citation needed (https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)] Mandarin then sent it to McCarran International Airport (https://en.wikipedia.org/wiki/McCarran_International_Airport) for storage.[citation needed (https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)] From April 2002 it was owned and operated by a religious organization known as Gospel to the Unreached Millions (GUM), headed by K. A. Paul (https://en.wikipedia.org/wiki/K._A._Paul), and was christened 'Global Peace One (https://en.wikipedia.org/wiki/K._A._Paul#Global_Peace_One)'. On July 17, 2005 the FAA (https://en.wikipedia.org/wiki/FAA) suspended its operating certificate due to insufficient maintenance.[citation needed (https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)] As of May 20, 2010[update] (https://en.wikipedia.org/w/index.php?title=China_Airlines_Flight_006&action=edit), the aircraft is kept in a large hangar at General Abelardo L. Rodríguez International Airport (https://en.wikipedia.org/wiki/General_Abelardo_L._Rodr%C3%ADguez_International_Airport) in Tijuana (https://en.wikipedia.org/wiki/Tijuana), Baja California (https://en.wikipedia.org/wiki/Baja_California), and is reported to be in very poor condition.

[FCeng84]

When an airplane is certified to a particular speed it is not only tested by going that fast in a calm air, 1 g maneuver. Demonstrations for Vmo also include maneuvering to limit load factor of 2.5 g pull-up and -1g push over when at those speeds. As you would imagine, the loads associated with these maneuvers are significantly higher than those for 1g flight at slightly higher speeds.


On the topic of the China Air 747, it was the 5 g pullout that bent the airplane. A well executed barrel role by itself will not take an airplane beyond its design load capability as load factor should not exceed 2.5g.


Commercial airplane flight tests are so heavily instrumented with data being recorded all the time that it is hard to imagine a test pilot getting away with an unauthorized barrel role today. In the past, however, I have heard rumors that pilots have performed barrel rolls with most models some time during flight testing. Tex Johnson in the 707 over Lake Washington during SeaFair was a little more public than most!

[westhawk]

the debris from the gear doors is what damaged the tail.Thanks tdracer, that makes good sense.

In the NTSB accident report it's also noted that the wings had a permanent "set" of 2 or 3 inches upward at the tips following the incident, still within Boeing tolerances for the type. And the APU broke loose from it's mounts. Any way you look at it, it's an amazing testament to the structural engineering of the 747 that it was able to tolerate such abuse without failing catastrophically.

It was calculated that the indicated airspeed of one of the 767's that hit
the WTC was over 460 Knots, the old girl stayed together as long as she could..
But when exceeding mach limits, there's more than just the dynamic pressure to be concerned with. Though many types may tolerate the forces applied to the airframe during operation beyond Vd, mach induced buffet/vibration associated with operation beyond Md can cause a host of other problems. Beyond a certain mach number, shock induced airframe buffet/vibration can render flight instruments unreadable, cause force reversals on flight controls and induce stress overloads in airframe structures.

The maximum demonstrated dive speed will be less than the speed at which any of these effects become excessive. All on an airplane which has not yet been subjected to the rigorous daily abuse associated with years of line flying and the minimal maintenance attention many airliners have to live with in the real world.

Just as a thought experiment, I wonder how a typical certification test pilot would react to the idea of being assigned to dive test a typical 737 with 20,000 typical airline cycles on it.

[vilas]

Most if not all of the damage to the horizontal tail was not due to aerodynamic forces. The landing gear uplocks failed and the gear deployed through the landing gear doors during the pullout - the debris from the gear doors is what damaged the tail.


Vilas, my memory is the same as westhawk - it returned to service. According to Wiki:
tdracer you may be right.If it flew again it's credit to people who put it back.

[tdracer]

I'm sure there are exceptions, but as a general rule (at least for subsonic aircraft) max airspeed is limited by dynamic pressure, while max Mach is limited by controllability issues primarily related to supersonic flow over the control surfaces.