Did I just see a Dreamliner go transonic (Mach 1.01)?

[AndyHagen 1]

Hi there,

Sorry if this is old news. This evening, I followed the Norwegian carrier B788 NLH82P flight from Oslo to Stockholm. I am quite sure this was an empty plane transfer flight. One of the reasons for this assumption is the speed.

During a 2431 fpm climb, it reached 596 knots / 1103 km/h at 30.849 ft. I am aware of the (un)accuracy of my Flightradar24-app, but this was stable. Even at 28.000 ft, it reached 594 knots / 1100 km/h.

In my book, 596@30.849 equals Mach 1,013. Also 594@2800 equals Mach 0,999

 

Something tells me this is not normal procedure, and must cause a certain stress on the airframe? Heavy tailwind?

 

Flight here:

http://www.flightradar24.com/2013-09-23/16:53/12x/NLH82P

 

Regards,

Andy

[Murmur 3,944]

I'm pretty sure those speeds are GS (ground speed). Mach speed is (by definition) relative to the air, not to the ground. So yes, there was indeed a heavy tailwind, so the aircraft was not exceeding Mach 1. :smile: No way an airliner could reach or exceed Mach 1 on cruise, maybe it could in an extremely steep descent from high altitude, but that would cause, at minimum, heavy structural damages.

 

[EngineRoom 205]

I think Murmur is correct - what you're seeing is the groundspeed, which is of course not what Mach number is referenced against.

 

I remember back in 1999 I was on a British Airways 747-400 and the in-flight map showed us travelling at 660mph at around 39,000ft. We weren't doing Mach 1 though... just a strong following wind.

 

I seem to recall reading a story somewhere claiming that a DC-8 reached Mach 1. I also remember reading something similar regarding the VC10. How true they are I don't know, but I have my doubts.

 

I believe officially the fastest cruising civil aircraft after Concorde was the Cessna Citation X. The fastest airliners I think was a toss up between the VC10, CV990 and Tu-154. I think the VC10 holds the record for fastest Atlantic crossing of an airliner after Concorde.

[AndyHagen 1]

Hi,

Thank you for your replies!

I just realized I have the AeroWX app, confirming a tailwind of 40-100 knts for the relevant area

So GS it is.

 

Regards,

Andy

[Tom Allensworth 1,532]

The aircraft is not designed to take the transonic buffet that occurs at just below and just through mach 1. Doing that would tear the wings off I am pretty sure.

[Propane 16]

Yeah, there's a jetstream over Scandinavia at the moment, around FL320. Flowing west to east with speeds up to 90kts according to the SIGWX chart right about now. It has some nice effects on the upper level winds. Today we were climbing with about 160KIAS and a GS of about 225kts. And that was just going up to FL150 (it was coming more from the North earlier today, nearly fully on our tail).

[Cessnaflyer 56]

Well technically they cruise in the transonic range. Transonic is between .8 and 1.2 Mach. That's not going to rip an airliners wing off. The first worry would be Mach tuck as the center of lift moves aft.

[EngineRoom 205]

I believe an aircraft in the trans sonic speed range already has supersonic airflow over localised parts of the airframe.

 

I think as far as a conventional airliner (at least one with a swept wing), other than the Mach Tuck and subsequent shift of lift, and all that means for trim, drag, and elevator authority,,, the big limiting factor is those big high bypass turbofans won't like a supersonic air flow at the inlets one little bit. Hence the majority of supersonic aircraft have means to slow down the air flow before it reaches the engine.

[vololiberista 205]

I think Murmur is correct - what you're seeing is the groundspeed, which is of course not what Mach number is referenced against.

 

I remember back in 1999 I was on a British Airways 747-400 and the in-flight map showed us travelling at 660mph at around 39,000ft. We weren't doing Mach 1 though... just a strong following wind.

 

I seem to recall reading a story somewhere claiming that a DC-8 reached Mach 1. I also remember reading something similar regarding the VC10. How true they are I don't know, but I have my doubts.

 

I believe officially the fastest cruising civil aircraft after Concorde was the Cessna Citation X. The fastest airliners I think was a toss up between the VC10, CV990 and Tu-154. I think the VC10 holds the record for fastest Atlantic crossing of an airliner after Concorde.

Indeed the VC10 was the fastest subsonic airliner after Concorde. It's normal cruise was restricted 0.84 but it was quite easy for it to go way above that. I know of one story of a medical emergency on a flight from S. Africa the pilot requested a higher FL and flew at 0.95!

[LeeL 272]

Didn't the A380 have to do some testing close to Mach 1? Did the 787 also?

[japascoe 98]

Didn't the A380 have to do some testing close to Mach 1? Did the 787 also?

All planes have to test up to Mmo (or maybe even slightly above I could try looking up the details later if you want). So that could take you pretty close to Mach 1.

[Cessnaflyer 56]

Didn't the A380 have to do some testing close to Mach 1? Did the 787 also?

An interesting little read. The aircraft will pass the Mmo in testing  

 

§ 25.253   High-speed characteristics.

(a) Speed increase and recovery characteristics. The following speed increase and recovery characteristics must be met:

(1) Operating conditions and characteristics likely to cause inadvertent speed increases (including upsets in pitch and roll) must be simulated with the airplane trimmed at any likely cruise speed up to V MO / M MO. These conditions and characteristics include gust upsets, inadvertent control movements, low stick force gradient in relation to control friction, passenger movement, leveling off from climb, and descent from Mach to airspeed limit altitudes.

(2) Allowing for pilot reaction time after effective inherent or artificial speed warning occurs, it must be shown that the airplane can be recovered to a normal attitude and its speed reduced to V MO / M MO, without—

(i) Exceptional piloting strength or skill;

(ii) Exceeding V D / M D, V DF / M DF, or the structural limitations; and

(iii) Buffeting that would impair the pilot's ability to read the instruments or control the airplane for recovery.

(3) With the airplane trimmed at any speed up to VMO /MMO , there must be no reversal of the response to control input about any axis at any speed up to VDF /MDF . Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed at VMO /MMO , the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC /MFC , but there must be a push force at all speeds up to VDF /MDF and there must be no sudden or excessive reduction of elevator control force as VDF /MDF is reached.

(4) Adequate roll capability to assure a prompt recovery from a lateral upset condition must be available at any speed up to VDF /MDF .

(5) With the airplane trimmed at VMO /MMO , extension of the speedbrakes over the available range of movements of the pilot's control, at all speeds above VMO /MMO , but not so high that VDF /MDF would be exceeded during the maneuver, must not result in:

(i) An excessive positive load factor when the pilot does not take action to counteract the effects of extension;

(ii) Buffeting that would impair the pilot's ability to read the instruments or control the airplane for recovery; or

(iii) A nose down pitching moment, unless it is small.

( B) Maximum speed for stability characteristics, V FC /M FC . VFC /MFC is the maximum speed at which the requirements of §§ 25.143(g), 25.147(f), 25.175( B)(1), 25.177(a) through ©, and 25.181 must be met with flaps and landing gear retracted. Except as noted in § 25.253©, VFC /MFC may not be less than a speed midway between VMO /MMO and VDF /MDF , except that, for altitudes where Mach number is the limiting factor, MFC need not exceed the Mach number at which effective speed warning occurs.

© Maximum speed for stability characteristics in icing conditions. The maximum speed for stability characteristics with the ice accretions defined in appendix C, at which the requirements of §§ 25.143(g), 25.147(f), 25.175( B)(1), 25.177(a) through ©, and 25.181 must be met, is the lower of:

(1) 300 knots CAS;

(2) VFC ; or

(3) A speed at which it is demonstrated that the airframe will be free of ice accretion due to the effects of increased dynamic pressure.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5671, Apr. 8, 1970; Amdt. 25-54, 45 FR 60172, Sept. 11, 1980; Amdt. 25-72, 55 FR 29775, July 20, 1990; Amdt. 25-84, 60 FR 30750, June 9, 1995; Amdt. 25-121, 72 FR 44668, Aug. 8, 2007; Amdt. 25-135, 76 FR 74654, Dec. 1, 2011]

[japascoe 98]

Well you would have to read the relevant Acceptable Means of Compliance (AMC) to check whether this actually has to be shown during a test flight or whether a simulation is enough, but I'm guessing (2) and especially (2)(iii) would be hard to do with simulation alone, rather than during a test flight.

[Cessnaflyer 56]

Well you would have to read the relevant Acceptable Means of Compliance (AMC) to check whether this actually has to be shown during a test flight or whether a simulation is enough, but I'm guessing (2) and especially (2)(iii) would be hard to do with simulation alone, rather than during a test flight.

I am not sure how the FAA treats it but here is one of the high speed AMCs I could find. It seems even with limiting devices they have to be switched off and tested like they failed.

 

http://www.easa.europa.eu/rulemaking/docs/npa/2011/NPA%202011-09.pdf

Well you would have to read the relevant Acceptable Means of Compliance (AMC) to check whether this actually has to be shown during a test flight or whether a simulation is enough, but I'm guessing (2) and especially (2)(iii) would be hard to do with simulation alone, rather than during a test flight.

http://www.easa.europa.eu/rulemaking/docs/npa/2011/NPA%202011-09.pdf

 

It looks like it has to still be tested even when limiting devices are installed.

[japascoe 98]

A couple of clauses in CS25 do say: ``The speed increase occurring in this manoeuvre may be calculated if reliable or conservative aerodynamic data issued.'' Though it's probably not possible to get accurate enough data without flight testing.