Mach overspeed 737-800

[InChina]

Hi , just want some thoughts on the following situation. This has resulted in the captain being demoted to FO, and myself (the FO) being suspended from flying for one month with no pay, so to us guys its a pretty serious issue and any thoughts or comments as to is the blame ours, some environmental impacts such as wind changes, aircraft not behaving normally etc.


We were cruising at 38100 feet (China) and the aircraft was a 737-800. The FO (myself was pilot flying)
Descended to 33100 feet 1000 feet per minute using VNAV descent. Then maintained altitude until we were 2000 feet plus above the descent path (captains memory) 1000plus feet above descent path (my memory) not sure of the exact amount.
Told to descend and started descent using VNAV, at this time we had a tail wind component of -25 knots and speed of Mach .78
Drag required warning came on the FMC, relayed to the captain who said no need for speed break because so close to descent path. For previous experience I did not see a problem. I then entered some descent information on the FMC. Looked up and saw a rapidly (very rapidly) increasing green speed trend arrow. Which resulted in a Mach over-speed warning.
The following is from QAR and our actions.
At 40 seconds after beginning decent vertical speed was 5400 feet/Min (we know its fast) with a pitch down of 5.6 degrees, speed Mach .784 . Tailwind component 25 knots. This is probably about the time I noticed the speed trend arrow and called to the captain “speed” or something to that affect.
then aircraft started to pitch up reaching .527 degrees nose down
At 42 seconds after the decent began the speed break was deployed. At that point the aircraft maintained the same pitch down rate of .527 for 4 seconds and the vertical speed actually increased by 400 feet per minute and the airspeed also increased.
Then the aircraft started to pitch up, but due to momentum the air speed still increased, but at a slower rate.
At 46 seconds after the decent began VS was engaged by the FO and a low decent rate dialled up.( this does not show on the QAR but both captain and FO agree it happened.
AT 47 seconds after the decent began the captain selected level change.
At 50 seconds after the decent began , at 29740 feet we had the Mach over speed warning sound at Mach 8.26, with a decent rate of 3400 feet per minute
At 51 seconds the speed was Mach .831 before the speed and descent rate rapidly reduced and the flight continued. The warning sounded for 6 seconds, with us being over speed for 2 seconds and equal to the speed for one second. Wind for the first 40 seconds was steady and gave us an effective tail wind of 25 knots. At 40 seconds this rapidly changed to a tail wind component of 45 knots in less than 20 seconds. We think the wind change contributed quite a lot to the overall situation.


Any thoughts, especially anything useful we can use in our defence. Also if the blame is totally ours then that something we have to accept. Thanks

[hetfield]

I'm not current on 737, so what is your MMO limit? What does the AOM say if this speed limit has been exceeded?

For example, on A300 there is only a maintenance action required if exceeding VMO+20 kt or MMO+0.02.

[Denti]

MMO limit is 0.82. The QRH basicly says to reduce speed if the speed is above VMO(340)/MMO. It would be a mandatory techlog entry and i would write a report afterwards as well.

Anyway, personally i do not like to use VNAV when more than a couple 100 feet above path because exactly this scenario can happen despite my fleetmanager telling me that flying VNAV has more protections than using simple airmanship. Level change with a slightly higher descent speed usually sorts out the tailwind and above path situation, if needed i can take the speedbrake as well. Approaching the path i can switch then back to VNAV. VNAV usually tries to aggressively recapture the path with up to MMO/VMO and with an additional sudden increase in tailwind you can easily bust the limit which is not really a nice thing.

The measures taken seem pretty harsh though.

[BOAC]

I would agree with Denti that the company actions as you have described them are excessive for what is a small exceedance.

Not sure if you have things like 'unions' to assist where you are, but I would look anyway at:

1) The Company Ops Manual/perceived company procedure for descending from high level ie VNAV to be used as primary tool?

2) If so, what guidance/warnings/training you are given on its use

As Denti says, 20/20 hindsight now will have you both using LVL CHG in future, and Denti's Fleet Manager is talking horse **** and would appear to have little practical experience of the a/c! 'Protections' in VNAV are virtually non-existent and what 'protections' there are are only effective when the old horse has bolted and not before.

[latetonite]

I agree with previous posts. It is however proof that aircraft still have to be flown, even in "reduced automatics", like LVL CH or V/S. Calling yourself a pilot on the B737NG if you are only able to set a new ALT in the window, pressing VNAV, then watch the show and not see that trend vector going past the "zipper"? hmmm..
Watever button you push, you should await the result and airplane`s response. And if necessary correct it.
It shows that too many pilots nowadays try to talk to FMC`s, and let them fly the aircraft. I see it on a daily basis, with identical results. FLY first!

[Andrén]

I wouldn't care about changing mode in that case to V/S or LVL CH. I would just pull the yoke back, let the airplane go to CWP.

It's the easiest and most effective way of getting the airplane to do what you want.

(or just press the magic button (auto pilot disconnect) )

[FCS Explorer]

also agree with previous. clacker comes on at .823 (i KNOW that :})
once above vnav-descend profile i (also) strongly recommend NOT to use VNAV to recapture as it will dive heads down for the path. while it is true that there are 'protections' the problem is that the auto-flight system installed works very sloppy. in some situations you can even get into over-speed with LVL CHG set to .82/340 as the auto pilot lacks preciseness.
or in other words: even if your entries on the MCP are 'in limits' the inertia of the system will bust those entries/limits. not sure what your employer makes of this.

[john_tullamarine]

I can only comment on the thread posts.

However, the event appears to be trivial so far as an Mmo exceedance is concerned.

Suggest you check your AFM for any oddball restrictions but, in general, Vmo/Mmo

(a) ought not to be INTENTIONALLY exceeded by the pilot, other than for

(b) authorised test OR

(c) authorised training.

A minor exceedance is a non-event and quite common during descent unless you are maintaining a moderate margin below the barberpole.

From the thead, I would suggest that one probably ought to have done something to control the VNAV excursion earlier and more positively but that's about it.

As a point of note, I think I only ever did one descent in VNAV (-300), wasn't impressed, and always flew the descent thereafter either in level change or, more commonly, handflew. Sounds like Boeing hasn't improved the toy at all ...

Refer to FAR 25.1505 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=e2d6ee74564b7efc97058fb3ca6c75f2&rgn=div8&view=text&node=14:1.0.1.3.11.7.198.3&idno=14) for information.

[InChina]

Hi thanks for the replies.
At this company we don't have any SOP so as a first officers we find ourself having to fly the way a particular captain wants, that means changing our flying style to suit the captain, landing with lots of power or no power depending on the captain, using Vnav/level change or VS depending on the captain. With this particular captain he likes Vnav so that's why it was selected as opposed to either level change or VS which I prefer....And before people say anything about CRM or pilot flying, if as first officers we don't do the flying as a particular captain wants, that captain will change the MCP mode so we have to fly the way he wants.
Anyway this is off the point, so please don't say how crazy that is, its just the way it is at this company.

What we are especially wondering is did we do anything against anything found in the Boeing manuals. Yes we know we made a bad judgement, but was the course of action actually wrong? Its my understanding that VNav should offer protection against busting Mmo. I know some people have said that that the Vnav protection is rubbish (and I now 100% agree with you) but as pilots have we actually done anything wrong by expecting the Vnav to offer protection?
As I stated we did spot the airspeed trend arrow increasing and we tried to correct accordingly. Again, our actions might not have been the best or as fast as needed, but were they actually wrong? The company are saying it's totally pilot error, nothing to do with the wind change and also that Vnav offers no protections at all.........
It should be noted that the time from noticing the airspeed trend arrow to busting the Mmo was 10 seconds, so in those 10 seconds when we were trying to slow the aircraft it was still accelerating.

Also we think the tail wind component increasing by 20 knots in such a short space of time was also a big factor and this is why the aircraft could not offer the Mmo protection.

You thoughts and comments please.... and I appreciate your constructive comments, +ive or -ive Thanks.

[ChristiaanJ]

Brief question/note, and probably not relevant....

There's a mention of an abrupt change in tailwind as a contributing factor.
Could that have been accompanied by an abrupt decrease in OAT?
That would cause a drop in the speed of sound, hence an increase in Mach number for the same airspeed.

Just asking because we ran into the same thing with Concorde.

The problem wasn't recognised until the route proving, because the phenomenon doesn't really occur at higher latitudes.
The result of the sudden increase in Mach number was a quite unpleasant pitch excursion as the A/P tried to stay within the M=2.04 limit.
The problem was solved in the end by a major modification of the Max Cruise mode, with both A/P and A/T being made to "do their share" to keep the aircraft inside the limits.

CJ

[KAG]

Drag required warning came on the FMC, relayed to the captain who said no need for speed break because so close to descent path. For previous experience I did not see a problem. I then entered some descent information on the FMC. Looked up and saw a rapidly (very rapidly) increasing green speed trend arrow. Which resulted in a Mach over-speed warning.
Were you in VNAV speed, or VNAV path on your FMA?


Using VNAV is objectively tricky to use.
Many pilots never use it during the descent, because even with a good understanding of the VNAV mode, many incident happens every year due to the use of VNAV during the descent (and approach...). VNAV has to deal with the flight path, speed, pitch, rate of descent, thrust all at the same time and autonomously as the situation evolves. Wrong wind input or altitude constraint will automatically result in the pilot adjusting the thrust (speed decreasing) or the speed break (speed increasing). As a result choosing VNAV for the descent should imply to take very seriouly a FMC warning "drag required", and a very close speed monitoring.

There's a mention of an abrupt change in tailwind as a contributing factor.
Could that have been accompanied by an abrupt decrease in OAT?
That would cause a drop in the speed of sound, hence an increase in Mach number for the same airspeed.
Very interesting indeed...

Cheerio InChina ;) good luck.

[TopBunk]

I then entered some descent information on the FMC

Don't be surprised then when the FMC is given 'better' descent info (w/v) that it may pitch down to regain the Vertical profile! Why were you programming the descent at that point?

At the end of the day, if you see a situation develop( like an overspeed), your first reaction should be to fly the aircraft (via a/p modes - select v/s or flch, or handfly) but not to reprogramme the FMC!

I'm sorry, but you have to remember who is in control, you or the computer. I have little sympathy for you (and even less for the captain).

Having said that, your operator sounds like a nightmare, but I'm sure you'll learn your lesson!

[BOAC]

I have for a long time (20 years) been convinced there is an underlying software 'bug' in the Classic/NG pitch A/P computations. To avoid diverting this tread I am starting a new one on this topic at B737 A/P pitch software - PPRuNe Forums (http://www.pprune.org/showthread.php?p=5556330#post5556330)

[stilton]

Agree with previous posters that you need to be more assertive about controlling the Aircraft ,not just wait for the automatics to fly it and then react too late.


However, demoting the Ca to Fo and docking you a months pay for a .06 Mach exceedance :eek:



That's quite unbelievable. I think I would be looking for employment elsewhere..

[skyloone]

VNAV is good at some things and franlky pretty poor at others. Now I know the saying input = output but I'd agree that its not always the smartest box of tricks. I never have understood why it'll happily dive into the clackers. For me as a rule, initially I never use VNAV when past TOD or above profile unless at a low enough altitude to have a good margin from the clackers. Even then one tends to get a dirty dive followed by a correction when at the path that results in an uncomfortable ride for all. If the situation is right use vnav but use speed intervent to limit the speed and hence the dirty dive. As mentioned in the tread before, use CWS if needs be. The slower descent may be a problem if a level restriction applies. If to be level by xyz can't be met without compromising the a/c handling say so and they'll have to negotiate another plan. ATC are not always going to realise the limitations you have to work with.

Think the company's response is less than positive. I would have hoped they would take the lessons learned and use it in the next round of training. If my memory is correct an engineering inspection is required if in the clackers for twenty seconds or more by X amount of knots. There is actually a good margin there before any damage to the wing skins is done.

Skyloone

[Mikehotel152]

Sorry to hear of your plight InChina.

I would agree with the comment's about VNAV's tendency to dive for the path regardless of speed and the dangers of hitting VNAV and assuming all will be well. I've seen the 'clacker dive' in the sim and on the line. We're taught to use LVL CHG and a chosen speed until back on path to avoid problems.

I should add that our SOPs require the input of best available info on winds during the descent, QNH and temp at destination and encourage regular reselection of the next WPT to update the winds in order to keep the path accurate. As always, one has to be very careful to check VNAV's actions after making any updates.

Our ops manual also mentions that you will see a CDU message warning of 'drag required' if an unexpected tailwind results in a significant increase in airspeed to maintain the path.

Unfortunately, it sounds like the scenario that caught you out. Company's reaction certainly seems OTT given their lack of guidance or SOPs.

[FlightDetent]

Adding tailwind component would initialy bring reduction in IAS/Mach, no? Only when the aircraft is "established" in the new layer of air it will deviate above (forward of) calculated descent trajectory. The increase in speed is a result of AP guidance attempting to regain VPTH if that is the active mode. Of course it should stay clear of the barber pole. My bet is on temperature change. The existence of air layer with different properties is exhibited by the sudden and significant wind change. Again, positive tailwind shear makes your airspeed drop, not the other way around.

FD (the un-real)

[safetypee]

In addition to BOAC's input, it is possible that the changes, particularly the combination and/or timing, were beyond the capability of the autoflight system – a design limit, which requires pilot intervention.
Autopilots have limited capability when adapting to rapidly evolving situations. Thus, when demanding a descent, the pitch channel will lower the nose and there is a tending to increase speed. Auto trim may subsequently run nose-down for the speed increase.
If the autothrottle is not well matched to the pitch command, then the thrust reduction (due increasing speed) is slightly delayed and when it occurs, may add to the nose-down pitching moment (force), which together with the new trimmed condition (also nose down force) may exceed the opposing auto pitch control (nose-up force), due to lack of autopilot ‘muscle’.
Thus, speed will increase until the nose-up control and delayed auto trim input (always delayed to prevent oscillatory motion) takes effect. During the intervening time, it is possible to exceed Mmo, particularly when cruising at high speed.

The effect may be more noticeable in VNAV if that mode uses a ‘soft ride’ feature – reduced autopilot ‘muscle’ and/or rate of control application, and also if the cg is nose-heavy and/or the airbrake causes an adverse pitching moimnet - often a dominant feature (cf Avro RJ operators).

The situation has to be understood as a limit in the capability of automation, which pilots are expect to know, detect, and correct, but which they might only learn from by encountering the situation – experience!
Thus the incident may have been a limit of expertise.

Blame should not be allocated; the situation is an opportunity to improve understanding. Thus, both the crew and the management should have learnt something – the crew about aircraft / autoflight limits; management about the need for training, and the need to gain experience – often via small errors.

We all suffer error, many occurrences during each flight. Generally, they are inconsequential because the source of the error is detected (understood) or the resultant, adjusted in time to avoid a consequence.

We should only worry about the big errors; most of those originate from management.
In this instance, it appears that the management error is the lost opportunity to learn – about investigating incidents, about aircraft systems, about human factors, and the concept of a no-blame culture.

P.S. If you ever consider the need to ‘override’ the autopilot, always disengage the system and fly manually. Manual flight provides a quicker and more precise feel for the situation; particularly for aircraft trim.
Some aircraft may have nasty surprises when attempting to mix auto/manual flight – the trim may run against you, and this can make the situation very much worse. The aircraft / trim muscle may equal your muscle!

[cosmo kramer]

InChina:
What we are especially wondering is did we do anything against anything found in the Boeing manuals.

To stictly answer your question - Yes as a crew you did:


OM B vol 2 chapter 11:

ADVISORY MESSAGE:
DRAG REQUIRED

CAUSE:
Airspeed is 10 kts or more above FMC target speed or within 5 kts of Vmo/Vmmo.

CORRECTIVE ACTION:
Use speedbrakes, trim or reduced thrust, as required, to bring the airplane within 5 kts of FMC target speed.

Since thrust was already at idle your only corrective action available according to the manual would be to use the speedbrakes. You did not do so accordingly.

InChina:
I then entered some descent information on the FMC. Looked up and saw a rapidly (very rapidly) increasing green speed trend arrow. Which resulted in a Mach over-speed warning.
This may account for the discrepancy between the recalled path deviation from you and the captain. If you changed e.g. an altitude constraint or descend winds, deleted a waypoint etc, the FMC calculates a new path. One of you may remember the old path and the other the new. If the new path suddenly predicts you much higher, the autopilot will increase vertical speed, maybe contributing to the pending overspeed situation.

As stated by many other posters I too would recommend to abandon VNAV at the moment DRAG REQUIRED is annunciated. This is another good reason to switch to LVL CHG when above the path and messing with the FMC, since you don't know witch immediate effect it may have on the flight path.

InChina:
As I stated we did spot the airspeed trend arrow increasing and we tried to correct accordingly. Again, our actions might not have been the best or as fast as needed, but were they actually wrong?
Before the overspeed condition, I would have pulled the wheel into CWS as some other posters also mentioned. But in the overspeed condition Boeing recommends to leave to AP engaged.

FCTM chapter 8, Non-Normal operation: Overspeed:
When encountering an inadvertent overspeed condition, crews should leave the autopilot engaged unless it is apparent that the autopilot is not correcting the overspeed. However, if manual inputs are required, disengage the autopilot. Be aware that disengaging the autopilot to avoid or reduce the severity of an inadvertent overspeed may result in an abrupt pitch change.
During climb or descent, if VNAV or LVL CHG pitch control is not correcting the overspeed satisfactorily, switching to the V/S mode temporarily may be helpful in controlling speed. In the V/S mode, the selected vertical speed can be adjusted slightly to increase the pitch attitude to help correct the overspeed. As soon as the speed is below VMO/MMO, VNAV or LVL CHG may be re-selected.
You did the right thing in switching to V/S. As can be seen from the above the captain incorrectly switched to LVL CHG. Maybe you can go free on this one, especially since the captain also declined your request for using the speedbrakes as appropriate according to the manual in the first place. But I guess it depends on your morale and if you feel that the captain asked you to operate the aircraft differently than you yourself intended and if this was the cause of this situation.

Good luck - especially in finding a better company. You seem like you have a good attitude, do not shy from your responsibility and have willingness to learn from this experience. All good qualities for an aviator in my opinion.

[Northbeach]

There are several things about the NG that I don’t like. One of them happens to be the tendency to over speed. I think Boeing is improving the software some. When we first got these things (NGs) we had many cases of crews over speeding coming out of altitude.

Sorry about the time off from work. It seems a little harsh to me; but then you are in China, it’s their airline, their rules, and their culture.

Hindsight is 20/20 so I will dispense with “you should have done…..” and “the manual says…..” and barking at you to “fly the airplane”. At this point it’s counterproductive, and the event is self-critiquing. There are known issues with VNAV in the NG. The NG will over speed in VNAV, the system is not perfect. Whose responsibility is it to keep this from happening; yours and mine (the folks who get paid to fly it). When the NG gets off VNAV PTH (does it frequently) and tucks into VNAV SPD it will over speed if given the opportunity, as you have unfortunately found out.

What did you have on the descent page, what cost index are you using? One suggestion would be to put in something like .76/280 in the descent page. Doing so should give you a larger margin. Another technique to consider is to start down early in VS (or “descend now”) and then transition to VNAV PTH.

I like the wings, engines, performance, auto throttles and the HUD on the –800. The flight deck ergonomics, 2-axis autopilot, elements of the FMS and the noise level leave a lot to be desired.

[kijangnim]

Greetings
One demotion and one suspension is a bit hard for a MMO incursion, what is MMO? it is simply 90% of demonstrated MAX speed achieved during to test flights and for which the aircraft is certified, in other word no big deal, did you exceed the Max certified MMO? NO you did not , so what is the issue?

[Sciolistes]

In China,

First, it is good of you to post your experience. I'm sure many will learn from it :ok:

My experience is Classic, so I should think we have more drag and slow quicker than the NG of which I have no experience. But maybe the similarities are similar enough. Also I think Kosmo is quoting a company manual.

I then entered some descent information on the FMC.
Did you exec the changes? One can get massive profile changes.

At 40 seconds after beginning decent vertical speed was 5400 feet/Min (we know its fast)
Yes, but even getting to 6,000 fpm hasn't presented us with problems. So that I doubt that in it's self is a problem.

Then the aircraft started to pitch up, but due to momentum the air speed still increased, but at a slower rate.
I have found that one needs to assert a zero pitch attitude to get any kind of meaningful decellerration near the limit. As others have said, the most expeditious and easiest way to accomplish this is gentle back pressure on the column to trip it into CWS P. My previous near MMO incursion I disconnected completely and although not an issue in anyway, required more chatter, more work generally so I don't see what is going to be gained by fully disconnecting the A/P.

t 50 seconds after the decent began , at 29740 feet we had the Mach over speed warning sound at Mach 8.26, with a decent rate of 3400 feet per minute
On the Classic, 3400 fpm is not enough to decelerate unless you intervene much earlier.

We think the wind change contributed quite a lot to the overall situation.
Unless you exec'd your FMC changes I don't think the FMC would calculate such an abrupt profile change.

In your defence the PF did extend the speedbrake but it was ineffective. Also, there is no specific guidance on what kind of pitch attitude or V/S would actually result in adequate decellaration. So you effectively had to suck it and see from which a minor incursion doesn't seem to be too bad a result. I would have done it differently, but then my company is a strong advocate of disconnecting the A/P if it's performance in insufficient. What is your company's written policy and how strongly is this reinforced in sim and line checks?

[Northbeach]

InChina,

I had a few more thoughts after reading through this thread again. It sounds like you are out in the frontier flying for a carrier that is trying to reinvent the wheel; no SOPs, PIC manipulates the flight guidance you fly whatever somebody else selects (sorry, but that’s weird), momentary exceeding of limitations brings harsh penalties, and as the FO having to be a complete chameleon adapting to every different Captain assigned as each conducts the flight in their own way (limited to no standardization).

It is not like the NG is a new frontier in aviation and flying a two pilot turbojet crew is some new invention; Aviation Safety Action Programs (self disclosure/no penalty in the interest of safety) standardized training and cultures of non-punitive atmospheres evolve over decades of learning what works and what does not work. In many ways it sounds like your carrier is choosing not to learn from the experienced gained by other carriers or understand how other well established carriers (from all over the world) conduct their flight operations. It sounds like your carrier may be trying to start from scratch. That is a tough way to run an airline. Part of the equation is most likely cultural, and that is a hard one as individual and national pride can be barriers to safety.

The other thing I wanted to mention was the VNAV PTH discussion. I did my share of knocking the system. But we still use it successfully every day. In fact we conduct RNP RNAV approaches to challenging airports that have limited, if any, conventional navigation approaches. The RNP RNAV approach is dependent on the VNAV PTH and it works well-extremely well! It seems like many pilots responding to your experience don’t use the system and descend in LVL CHG or VS. I was surprised. We use VNAV PTH successfully every day. Having said that I will admit that there seems to be an issue with the NG nudging, and going into, the over speed clacker at high altitude. It seems to be a problem up in the middle FL300s and above.

You got burned using the system, and that may lead you to never use it again. That’s your choice of course. I criticized the system, because it is not perfect, but I still use it and in many cases rely on it. VNAV PTH works fine for me, it just needs to be monitored (should not be a surprise). You can fly any way you want to. However I did not want my post to leave the impression that VNAV PTH was completely unreliable, always prone to over speed, and should be abandoned as a means to descend. Like I said we use it successfully all the time (140+ airplanes; 1,400+ crews).

[Sue Ridgepipe]

I find using VNAV PTH in China can be a very labour intensive operation. In fact I could probably say that about any descent to an airport in Chinese airspace. At one particular airport we go to it is not uncommon to be denied descent clearance until 10 or 20 miles past TOD, and then have to descend with a 50 knot tailwind and try to regain path. All this from a cruise altitude of 22600 feet, so large speed reductions prior to TOD are generally the order of the day.

Other places are the complete opposite where they will have you descending sometimes up to 150nm prior to your normal TOD and telling you "descent rate more than 2500fpm".

So the opportunities for using VNAV PTH for descent I find are very limited but when you do use it you have to watch it very carefully and be prepared to change modes or fly manually at any time.

[InChina]

Hi, thanks again for the replies. Some of them are very interesting and helpful indeed.
Someone asked what cost index we were using, it was 30 but I don't think that has any effect on this particular scenario as we were in Vnav path not speed mode.

As for the information I entered into the FMC it was in the forecast page, just the airfield temperature deviation and QNH. I didn't enter any winds, the reason I asked what effect the wind would have was because in the ten seconds before we exceeded Mmo the tailwind component increased by 20 knots. I was wondering what effect that would have had on the aircraft flightpath while it was trying to slow the rate of descent and therefore stop the increasing speed, I'm thinking that contributed to the over-speed, but some replies hinted it would contribute, some said it wouldn't so I'm still not sure??? Any more thoughts?
I've checked the QAR and there was no large temperature change accompanying the wind change, so the increase in Mach number due to temperature can be ruled out in this case, but its very interesting information, thanks for posting it.

Northbeach your comments about this company were spot on, are you sure you don't also work here?
Sometime last year an aircraft in this company had a tail-strike, and as pilots most of us still don't know the exact circumstances regarding it. The local pilots in the company were actually enjoying themselves and laughing about it, the punishment and pointing out the mistakes/misfortune of others rather than asking the pilots what happened and learning from it so it could be avoided in the future. Instead the pilot leaders seem to enjoy imposing unless punishment.

As for this situation the behaviour of Vnav descent,I'll put my hand up, it caught me by surprise and its one of the reasons I posted here to try and get some more information. Its not a mode I've used much, I have more than 1500 hours on the 737 all at this company and I can truthfully say I've used it less than ten times and I've certainly not had any guidance or training regarding this. Sim training at this company is more to do with aircraft handling than operational level training. I can happily disengage the auto flight and flight directors and fly manually from 10,000 feet, we are allowed to do it regularly. In the sim we practice things like pilot incapacitated with an engine failure, but we certainly do not do any training regarding CRM or something that would have prepared me better for the Vnav behaviour. Most of this type of “training” is done by myself using the Boeing manuals etc. Also remember no SOP's at this company.

With regards to this case the airline safety board is reviewing the decision and hopefully it will be overturned. The captain I was flying with that day is a senior captain in this company and I've recently been told the chief pilot pushed the initial decision through for “political” reasons. Then two days after the chief pilot pushed our punishment through he took off with no flaps so it will be interesting to see what happens in his case. Anyway I've moved way off the point of my post...................

[BOAC]

My goodness me, InChina - what fun you must be having:confused: I assume your CP will soon be an F/O?

A few observations which may help you:

Cost Index is relevant - VNAV path will 'attempt' to fly the appropriate speed for CI30 in descent as a target.

I spent many years on 3/4/5/700 filling all the boxes on the descent page, including inside leg, collar size, date of birth, to find it STILL screwed it up:ugh: I gave up and put nothing in the box UNLESS there was a tailwind for the descent to avoid the T of D being calculated 'too late'. IF there was a tailwind, that amplified your problem putting you much closer to Mmo.

I would recommend to you, if this 'culture' of doing it 'the Captain's way' exists as you say, that you politely decline if you are unhappy - no major issus - you may be thought of by Cpt X as a 'chicken' or whatever - so what?

If you are in a position where you have to do it in VNAV, I always found LVL CHG with a sensible speed entry was a better option down to below 30k. Generally except for howling tailwinds or really late descents, the 'drag required' can be ignored (provided the speed is controlled) and the path picked up later in descent where there is a greater speed margin as said above - all this, of course, subject to any fixed altitude constraints

Have in your mind where it SHOULD descend for the expected wind conditions and chosen speed etc, and if it does not agree, fly it your way.

Good luck!

[Northbeach]

InChina,

I am glad you found my synopsis useful. No, I don’t work for your company nor do I live in China. I am not a Chinese expert at all. I have spent a little time in Africa and the Middle East so I may have a “little” understanding of the challenges you face.

Your cost index will contribute to your problems. A cost index of 30 will result in a higher speed and steeper descent path than a cost index of 10. Therefore, when you go off path (it will happen) and into SPD you will be that much closer to the clacker. A few degrees off standard ISA, a bump of turbulence and you have an excursion. Lowering your cost index is not a silver bullet that will solve this problem. But it will give you more of a margin between the FMC derived descent speeds and the clacker.

Tail strikes on the -800; yes it can happen. Our most recent case was on a long flight with a heavy aircraft, a medium length runway and a disconnect from what the actual flaps were set at for takeoff and the V speeds (V speeds set for one flap setting, the flaps actually set at a different setting).

[rudderrudderrat]

Hi InChina,

just the airfield temperature deviation and QNH. Changing those values forces the computer to recalculate the descent profile. If it now thinks you are slightly high on this new profile, it will stupidly increase ROD in an attempt to capture the new profile rapidly. If the Barber's Pole is close - it's so easy for it to over speed. LVL CHG would have been a better mode until the margin was bigger.

Keel hauling crews for this sort of error is not the best way to educate them. I suspect there will be some floggings next - to help improve morale.

[homerj]

Hi In China,

Firstly congrats on a great post, albeit in aweful circumstances.
Anyone here who says that they have no sympathy for you is an idiot. Mabye its a culture thing but that punishment is simply ridiculous and I wouldnt accept it.

If I were you, id go on the attack.

Do the responsible aviation authority know about the lack of SOPs in the company you work for ?
Did the company train you sufficiantly in the use of Vnav?
Do the company have any other safety issues that you could remind the chief pilot that the aviation authority or even the press would be interested in hearing?
Mabye talk to an aviation lawyer.

Dont take it lying down , what youve described is a minor incident made more complicated by procedures, or lack of that the company failed to put in place.
These people get very nervous when you turn the tables and play the safety card.

Good luck , and let us know how you get on

[Rananim]

3 things:
-normal reaction for Chinese or asian airlines
-unintentional overspeed that is immediately corrected is not an issue,just like a single "glideslope" on approach that is immediately corrected..but in asia,they dont see it that way..very SOP-oriented..they take things very literally..you got one warning,ergo you were unsafe.No understanding of airmanship..common-sense and individual thought frowned upon.There is one way to fly the plane..the way described in the book.They've killed a lot of people in crashes..its a nervous environment and they want rote automatons not pilots with airmanship.
-vnav is over-rated...vs is the best AP pitch control offering smoothest flight to crew and pax but is disliked by many who dont know any better.

[InChina]

For those who are interested this was the reply we received from Boeing.

We have looked at the data you supplied and from the information we reviewed, we think that this is an airplane issue and not a flight crew error. Both (a captains name deleted) and I feel that the flight crew should not be punished for the brief overspeed on this flight.
Best regards,
(A Boeing Captains name deleted)

Deleted names obviously by me.
Safety review meeting to hear our appeal is tomorrow. I'll let you know the out come.

[piston broke again]

Sorry to hear both of you are put in this situation...it sucks and I don't think either of you have done anything beyond Boeing SOP's.

I offer this only from my own experience, take it or leave it. I hope it helps someone who reads it...

VNAV path is good only when little change is expected in the wind on descent and/or when your cruise mach is well below Mmo. (say 0.76)

If you have a really strong headwind or tailwind I would always use VNAV speed. VNAV path, although good, never gives you that protection quickly enough. If I have 100 kts tailwind component at upper cruise levels, I descend early by 10% of that TWC. (ie 10nm) in VNAV speed. If its a HWC, 10% late. (I just use time to measure it - ALT HOLD before TOPD then when the chinese glideslope appears, start the timer...If you are doing say 480kts GS or 8nm/min, then start you VNAV speed descent 1min 15 sec after the slope appears, for the headwind, before for the tailwind.

This my own rule of thumb and everyone has a different way to do it of course but I find it picks up the profile by 15-10,000'. Then use VNAV path from there as most of the height restrictions on a star are generally below 10,000'.

It never is an exact science and I'm constantly learning new things. Hope it all works out...

[Sciolistes]

InChina,

Well that is pretty conclusive from Boeing. Keep us updated, we're all rooting for you mate :ok: