Descending at vmo

[Captain Smiley]

It is a common practice at the airline I work for ( turbo prop) for pilots to descend the the aircraft in vertical speed mode but allow the airspeed to increase right up to vmo. Of course the overspeed horn sounds occasionaly. This is corrected immediately but normally laughed off as "who will be buying the drinks."

I don't really agree with this practice but I am surely in the minority. I've expressed my concerns to the CP but to no avail.

Do you see much need for my concern?

Thanks.

[Gary Lager]

I don't see any mention in Capt Smiley's original post of anything to do with O2 or the need for 'fast' descents, so the following comment is based on the assumption that we are talking 'normal' operations (i.e. non-emergency) here.

My concern is that if the overspeed clacker sounds, the aircraft has operated outside it's normal operating envelope, and at the very least the tech log needs to be annotated to that effect and the relevant Air Safety Report (ASR) filed. If this is not being done (i.e. the problem is just being 'laughed' off) then we have on our hands a bunch of unprofessional individuals who need to be properly re-briefed as to their responsibilities as professional airline pilots.

[LOKE]

You have exceeded an Aircraft Limit. Techniquilly speaking, you are supposed to write the aircraft up - unless you can find somewhere in the Regs an allowance in time or margin of exceedance - and I don't think you're going to find that. I'm not trying to be a stickler and I'll say that I've heard that noise lots of times and not written it up. It's just that if you have an Inspector on board and he hears it all the way down with no concern or action by the crew - you might be hearing from him.

This was dixcussed in a thread about flying in the vicinity of high moutain waves in larger jets with lots of inertia. It's possible to get the horn for a a relatively long period of time if - even when the throttles go to idle - if you fly into one.

LL

[Plain Driver]

An overspeed warning is an exceedance of set limits (Vmo / Mmo) and therefore should be reported in the Tech Log - that seems to be perfectly clear to everyone. That, of course, is only the follow up.

Remains the question: is there any need for concern when someone decides to descend in VS mode? It largely depends whether you have Auto Throttle to take care of (over-)speed problems. As most (all?) turboprops lack A/T systems, their pilots have 3 or 4 modes of descent at their disposal: Vertical Speed (VS), Indicated Air Speed (IAS), Basic Pitch and sometimes Vertical Navigation (VNAV).

VS mode: Fixed Rate of Descent. There is of course the airspeed indicator needle to monitor more closely as you have just given it permission to wander about its scale.

IAS mode: Fixed Air Speed. Vertical Speed now needs the extra monitoring, as either very low and very high descent rates are possible. The power levers (at least on "my" type of machinery) need a very delicate touch to make this a comfortable ride. Also, I have seen overspeed warnings with Vmo minus 5 programmed into the flight director.

Basic Pitch - both VS and IAS are on the loose here, so the amount of control over the aircrafts' path feels limited. Maybe just my feeling...?

VNAV - follow 'glide slope' type of FMS generated path in space. Both VS and IAS are let go of, but as VS is shown in the FMS monitoring is easy.

Personally (turbo prop jockey, too) I do not think that VS is a mode to be avoided, actually, I do it almost every time. My only other realistic option is VNAV. Just my two cents worth of course.....:uhoh:

[DCDriver]

and when I started flying, at TOC we were shown to let the a/c accelerate until we rang the bell, and then milk the throttles back until the noise stopped....
maybe I've got it wrong all these years...

[Captain Stable]

What I used to do was to descend in V/S until just below Vmo/Mmo and then switch to IAS mode to ensure we didn't overspeed. Similarly in the climb, used a comfortable V/S until a suitable point and then use IAS at the speed I didn't want to go below.

Sounding the overspeed clacker/horn/whatever demonstrates a lack of sufficient scanning/monitoring, IMHO.

On some aircraft (the ATR being one I've noticed most) there is a fairly constant difference between the Captain's and F/O's ASI's. If taking the speed to close to Vmo/Mmo this needs to be remembered. On the ATR the Captain's is normally the higher, and the Overspeed horn is linked to this, so it is incumbent on the F/O (if he is PF) to make allowance for the difference.

[john_tullamarine]

Vmo/Mmo is more a target limit in that the pilot is required to not exceed the value intentionally other than where authorised for training or test purposes. See FAR 25.1505 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=20880cf49fa3ea42614471be3cacf1fd&rgn).

Short interval excursions of a few knots are to be expected on occasion and are not going to rip the wings off ... However, if the air be bumpy one probably would be well advised to carry a small pad below Vmo.

However, I have to agree with my colleague ... for a competent instrument pilot, getting the clacker should be an infrequent event.

[Whaledog]

Well, most pilots are paid by the hour, So why are you burning more fuel, (Delayed opt. decent) while at the same time reducing your paycheck?????