I happened across a video this morning which claimed to list the top ten fastest commercial aircraft, although why it mentioned the Boom supersonic aircraft which hasn't even reached the prototype stage, I can't say. It reminded me of descending into Hong Kong in 1993 in a 747-400. The in-flight display showed that the air speed reached 1065 kmh and the aircraft was shuddering in an unusual way. I recalled in Chuck Yeager's autobiography mention of shuddering just below the sound barrier, but that speed is about 1200 kmh. Wikipedia lists the airspeed limit of the 747-400 as 1004 kmh.

I wonder what was happening here? Did the pilot exceed the airspeed limit of the aircraft, or was the in-flight display telling fibs? Was the shuddering possibly a feature of the high speed, or coincidental turbulence?

PS The "top ten" listed the Tu144 as the fastest-ever commercial airliner which I believe is true, although the list changes if you insert the word "successful" into the requirements. The Tu144 was a brilliant design in many respects but wasn't a commercially viable airliner, while Concorde was commercially viable for many years. I'd argue that Concorde was doomed by the inability to fly at supersonic speed over land; the only regular flights were the transatlantic route.
PPS Some might say that Concorde wasn't ever commercially viable. I'd put this in the same category as low volume regional city destinations - some services should still be operated at a loss, supported by more profitable routes. There's little balance in ticket pricing these days - the profitable routes are cheap and the unprofitable ones are expensive.

It was more than capable of flying supersonic over land, it's just that a certain group of "concerned citizens" spread rumours that a sonic boom would knock over cattle, curdle milk, change the channel on your TV and make people vote Republican. Well I think it was something like that, whatever the accusations there was no truth in the rumour they were anyway connected to US aircraft manufacturers or their families.....

The actual plot was purely political, the last thing the US wanted at that time was a non-US aircraft showing up the home grown offerings. Bah humbug

We could have had a much faster journey from Sydney to London too, except for a similar scare campaign. I saw Concorde fly over on the one and only visit to Sydney. It was a beautiful machine. I always wanted to fly in it, just once, but now that can't happen. I saw it in flight over Paris, and on the ground in Singapore and Heathrow. Sadly, the US SST program was doomed to failure because it had to be faster and carry more people. I don't think we will see supersonic commercial flight again soon.

Odds are it was merely the effect of having spoilers extended in a high speed decent. It's difficult to 'come down' and simultaneously 'slow down' in a jet without extending spoilers or speed brakes when ATC requests a slam dunk.


True Airspeed (TAS) is significantly higher than Indicated Airspeed (IAS) at altitude.


High speed (mach) buffet is a very different feeling and rarely encountered unless in an emergency descent (did the masks drop?) or performing an extended evasion maneuver.

You may be right, although I'm sure I checked the wing and the spoilers weren't causing the vibration I was referring to. Thinking about it now, I have since felt a similar vibration on a flight from Frankfurt to Barcelona, which was apparently some sort of clear air turbulence - or perhaps wake turbulence? The turbulence on the flight in Europe wasn't during descent.


So the true airspeed was even higher than the rated maximum speed?


Fair enough. The Mach buffet described during the attempts to break the sound barrier were violent (Geoffery de Havilland was killed by it), not the sort of vibration which occurred on the 747. Obviously I've never actually experienced supersonic flight. I was just curious because the speed seemed unusually high, and the vibration didn't seem to be caused by air brakes (which was obvious because you could feel that starting and stopping, aside from looking at the wing). The only time on the flight when things above in the cabin moved was when the aircraft touched down rather heavily at Kai Tak and quite a few of the overhead bins popped open (this was in 1993).

What was your source for the speed? If a typical passenger info display it would either be TAS or Ground Speed (GS). Highly unlikely the acft would be intentionally operated outside of its operating limits. I suspect the speed you saw was TAS.

One plans, flys and navigates by True airspeed, but what the acft 'sees' is the indicated speed (IAS) sensed via the impact pressure in the pitot system. As you go up the air density decreases so the airspeed shown on the airspeed indicator is lower than the true speed through the air (TAS). Calculations based on altitude and temperature translate IAS into TAS.

Above a transition altitude jets set speed as a percentage of the speed of sound (which also varies with density altitude) and also provides a direct means of avoiding Mach boundary performance issues. Mach buffet may be anything from a slight nibble to a nasty bite. Mach-plus jets slip through that zone with no buffet but normally experience a pitch trim change as the shock wave boundary moves.

The DC-8 is the only non-Mach airliner I know of ever certified at Mach-plus as it accidentally crept up to M 1.01 in a dive during certification testing at FL 410. You could point the A-6 Intruder straight down even with clean wings however, and it just bogged into its own bow wave at about M 0.9.


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Right, it was the passenger information display. Sorry, I read what you said backwards in effect - so the airspeed was slower than the ground speed indication, presumably due to a tail wind. Likewise I doubted that the aircraft would be flown outside its operating limits, but that's also why I found the high speed indications surprising, and the vibration disturbing at the time.


OK, makes sense.


Presumably aircraft which are designed to be supersonic experience no buffet precisely because they're designed to avoid it, while during the development of the aircraft to initially break the barrier, they didn't know how to design such a plane.


Wow! I didn't know that. I only flew on a DC8 once, when I was six years old.


That makes sense, given the design of the A6. Thanks for the discussion about something which I'd been curious about since 1993.



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Highly unlike that the 747 dived with near supersonic speed. Keep in mind though that the Mach speed is dependent of the altitude, the temperature and the air density among other parameters and that at ~30000 feet is less than 1100km/h (around 1090) so you might have gotten close to mach speed at that dive

I know it's highly unlikely, and I knew that the speed of sound changed. I was just curious about the displayed speed and the odd shuddering of the aircraft.

I suspect Orville might've said something like that to Wilbur over a century ago.

I It's always fun to discover new insights into topics of interest. I know when I've stumbled on one of those occasions when I discover I'm grinnin' like a fool an' smackin' my forehead to a chorus of "Duhs!".

Now if I could just find a really good clue about good whiskey, financial investments and the female of the species . . .

Ground speed's funny that way and, fortunately, wings pay no attention to GS.

A long time ago (1965) in a land far away I recorded a ground speed of minus - 18 kts at 14,000'. We were doin' about 200 kts in a wicked jet stream south of Japan in in a WC-121K on a typhoon recon mission that day.




The US ran into the same factors there with B-29's in WW II. Caused us to infiltrate 'special ops teams' (by donkey caravan no less!) into Siberia to establish weather monitoring stations. Wasn't just for air nav though; someone was astute enough to wonder about jet streams and drifting nuclear fallout.

Maybe!




Savour them, respect them, and enjoy them?

Fair enough. I've heard jokes in Australia about the crows flying backwards.


Presumably you would have changed course to establish a positive ground speed rather than burning fuel going backwards?
That's quite a modification of a Super Constellation by the way!

You remind me of a talk by Peter Hillary (son of Edmund Hillary) about the difficult decision to turn around before reaching the summit of K2. A those altitudes, the mountaintops are in the jet stream. He nearly died trying to get back down the mountain - eight other climbers were blown away and never found.


I hadn't heard of that before. I wrote a short story in high school where people in the southern hemisphere looked on as the northern hemisphere was destroyed in a nuclear conflict, but in University I learned that a nuclear winter would affect the whole planet.

The seat back displays I'm pretty sure are ground speed based. I 'cruised' back from Perth to Adelaide recently on a 737 at a leisurely 1100 km/h plus as shown on the seat back displays. We can get a howling NW jetstream down here in late winter.

The speeds shown on FlightRadar24 and similar sites are also look to be ground speed based. I looked my flight up on landing and it showed long segments at 1143 km/ h or thereabouts. Another jet going the other way (westwards towards Perth) was showing low 600's km/h and was down at 26-28000 feet trying to avoid the worst of the jetstream. My eastwards flight was 34-38000 feet to maximise the wind assist. The wind knocked about 20 minutes off the scheduled in air time and the schedule for the east bound flight is already 20 minutes shorter than the west bound schedule.