I've never had the clacker in my thus far relatively short professional career.

One presumes your operation descends with a margin to the barber pole. No problem there. I'm a bit dated but we routinely had minor clacker exceedances (I'm talking 5-10kt rather than a significant exceedance).

Any activation of the clacker is mandatory techlog entry, a call to maintenance and hopefully a deferred defect and authorization to continue.

With the greater emphasis on DFDR/QAR exceedance monitoring, that makes good sense as it indicates attention on the flight deck and adherence to SOP. I would be extremely surprised if the base response was other than to continue.

some airlines treat an exceedence whether it is over landing weight by 1 pound or over VMO by 1 knot as almost the end of the world.

That, of course, is both true and most unfortunate. Unless those monitoring exceedances have a suitable engineering/certification background, there needs to be plenty of guidance from the totem pole folk as to what is, and what is not, terribly important in the overall scheme of things.

As a pilot who can expect to be demoted or severely admonished, it becomes a big deal.

Absolutely correct .. we all have our crosses to bear unfortunately


The main value of this thread is to get the acceleration deterioration at height message across to the general heavy aircraft pilot population ...

Boeing have a current bulletin out for the NG, recommending that thrust not be brought back below 60% N1 for short term speed excursions & to use speedbrake if required.

The engineering manual at our joint requires a rather involved inspection for overspeeds greater than M0.02, which isn't much of an overspeed. It's 15kts for a VMO overspeed, if I remember correctly.

I just recently had an over speed in the cruise CAS went from 247kt to 272kt (.85 Mach)in 3 seconds due to a 6deg temp drop in that time. Pulled the speed brake but speed was still increasing so also pulled thrust back towards idle. Yes it does seem to take forever for the engines to spool up again, but speed never fell below what was bugged.

Yes, you just got to anticipate when to add thrust again. Then it's no problem, i.e. NOT wait with adding thrust again, until speed is back at bugged speed, but rather as soon as the speed starts decreasing again.

And of course not overreact for small speed excursions as Boeing writes in their bulletin. Keep calm. Rather a little too fast, than a little too slow. ;)

I am with you in saying that it is not a fall-off-the-sky deal, but I wouldn't downplay it to that extent.

The margin set between MMO and MD (cleared for flutter and loads) is not based on the crew assumption that MMO is a rubber-stamped line.

I am not saying to disregard MMO, obviously. I am just saying that unintentionally exceeding it is no cause for panic (unless you work for an airline run by people that have no understanding of aviation and will use any excuse to punish you).

MMO is just a line drawn on a piece of paper in some manual that someone had to give an approval stamp

Vmo/Mmo is a limit the same as any other and is required to be observed. However, the limit has a lot more fat than the older style certifications using Vne.

Indeed, most (not all) AFMs have the rider that the limit may be exceeded for test or training.

I was just reviewing a 747-8 AFM revision (something I need to do with some regularity), this is what it says:
"The maximum operating limit speed shall not be deliberately exceeded in any regime of flight."
I think the key word here is "deliberately".
BTW, 747 MMO is 0.90 Mach. During the 747-8 certification, I looked at a whole lot of data that was 0.97 Mach and higher (flutter testing and the such), and the airplane didn't break :ok:

I believe a key differenciator for test pilots is that they act in a particular way when they know the first or even the second hole in the cheese is lined up already.
This is why you will not find MD published in the AFM.

Test pilot during acceptance of new aircraft demonstrated MMO exceedance. No big deal at MMO + 0.2, apart from noise of the damn clacker!

Yeah probably a good thing what with 1% of pilots being clowns and all.
Do Boeing and AB use the same process for determining MMO relative to MD?

What is the term "MD" being referred to here?


Oops. Disregard. Just googled it. in case anybody else was as ignorant as me: Vd/Md are the absolute maximum speeds. I think referred to as dive speeds. 0.96 apparently for an A320, probably something similar for a 737.

Maximum Mach in a Dive...

Kfuddle
A320 VMO350KTS, MMO M.82, VD381KTS and MD.89.
Only A380 has MD M.96
According Airbus
1. critical loss of lift due high Mach is well beyond the normal envelope and MD.
2. In level flight at high altitude, drag increase prevents MD from being reached. In flight tests MD is reached through specific manoeuvres (dives with full thrust are necessary)

Thanks Vilas. So the difference between 0.82 and 0.89 isn't really that great considering the shear that can be experienced crossing a jetstream!

I think you overestimate the shear of even a very strong jet stream. Going from .79 to .85 (like I described previously) was a huge speed increase. And it took time. Had the speed continued to increase, it would have been fairly easy to pull back on the yoke an climb a bit.

Anyway, an Easyjet 737 was recorded to go 450 knots, in a botched manual reversion test. No damage to the aircraft afterwards! Though the Mach number was probably relatively low, as it happened around 10-15k feet, it is still a testimony, that these machines are stronger than what you might think.

And for those that think I am making that up/are not familiar with the incident:
http://www.aaib.gov.uk/cms_resources...JK%2009-10.pdf

It's an interesting read...

Deefer dog, I sure hope you meant +0.02 Mach, not +0.20 Mach :eek:


Most airliners don't like going supersonic :}

Thanks Cosmo,

You're probably correct about my over estimation, it would be something like 40kt increase from 0.82. However, we know how astonishingly quickly things can unravel at 40,000 once problems occur.

Thanks also for the report, the FDM recorded max was an astonishing 429kts! This was quoted as Mach 0.719. I guessing the FDM sampling rate is the reason why the pilot noted a higher speed. Looking at this "Diving" Into A320 Diving Speeds the A320 Vd is 381kts, which must be similar to the B737!

Check you this video of the A380 flutter tests (also at the end of the linked blog)

Speed brakes are not necessarily the best solution to an overspeed for all aircraft types. At highish levels, like 410, aggresive airbrake usage will easily take an aircraft like an E190 to the other end of the speed tape and beyond, without a significant change in airspeed. But reducing thrust to idle will provide relief. Fortunately, E190s have such small engines that they very quickly spool up to cruise thrust from idle.

PM