Ask The Pilot

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Investigation: AO-2017-092 - Operational event involving B737, VH-VUE, 78 km ESE Adelaide Airport, SA on 13 September 2017

Which autopilot mode were they in?. Vertical Speed?

 

[andmiz]

Which autopilot mode were they in?. Vertical Speed?

Not likely. Likely a FMC managed descent mode (VNAV PTH or VNAV SPD) and the overspeed may have occurred due to shifting wind and/or turbulence. Vertical Speed is generally (with exceptions) not a suitable mode for that distance out from landing.

 

[AviatorInsight]

Investigation: AO-2017-092 - Operational event involving B737, VH-VUE, 78 km ESE Adelaide Airport, SA on 13 September 2017

Which autopilot mode were they in?. Vertical Speed?

Like Andmiz mentioned, it would have been an FMC descent mode. For an overspeed event, it would have to be VNAV PTH. This is where the FMC disregards the speed to maintain the preprogrammed flight path. Vertical Speed mode does work in a similar way, but lots of changes would be required by the pilot to stay on the path.

 

[Altair]

How long to various elements of an aircraft last?
Would the engines that are fitted to a new aircraft remain for the life of the aircraft? (acknowledging their maintenance throughout their life)
How often are wheels replaced?

I am trying to find the link to the Forum that had the answer but unconfirmed answer is "No". Engines are progressively changed out so that each engine would have a different number of hours on it. This is due to limiting the risk that an engineering/manufacturing issue, in particular if it is a time limited part, could take out all the engines at the same time. So for example, JQ 787 when aircraft 2 was prepared for service they could have swapped one of the engines from the first JQ 787 (it all depends on how many hours were on it).

 

[jb747]

How long to various elements of an aircraft last?
Would the engines that are fitted to a new aircraft remain for the life of the aircraft? (acknowledging their maintenance throughout their life)
How often are wheels replaced?

The exact amount of time any element of an aircraft is in place isn't something we can see in the tech logs. Engines can be in place for a long time (four or five years), but I will eventually be pulled off for their own deep maintenance. That will be affected dramatically by the conditions they operate under. Sand, in particular, will shorten the time they remain in place. The oxygen bottle that went bang had been in use for 12 years, and had been on four aircraft in that time. Tyres are replace as their condition demands.

 

[jb747]

Investigation: AO-2017-092 - Operational event involving B737, VH-VUE, 78 km ESE Adelaide Airport, SA on 13 September 2017

Which autopilot mode were they in?. Vertical Speed?

There are a number of vertical (descent) modes, and they all have their particular place amongst your options. And most have some negatives.... Lateral and vertical modes are different animals, and you could be in a managed lateral mode whilst in a manual vertical.

VNAV PATH is the most common. In this case the aircraft will attempt to stay on the vertical path built in the FMC. It uses power as necessary to remain within a speed band, but once it hits idle, a steep path or wind change can cause the speed to drift outside of the range, in which case it will shift to VNAV SPEED. In that case it will hold on to the programmed speed, but will lose the path. It will recapture it if the opportunity arises. Selecting a hard speed on the MCP will also cause this mode shift.

FLCH, or flight level change, is a mode that you have to engage, and which will control the speed to a target using pitch. On descent power will be roughly idle. For small descents, the power will be chosen to make the operation happen in about a minute.

V/S is a mode that controls sink rate and speed. Power is used to control the speed, whilst the pitch is used to manage the sink rate. If you select too large a sink rate, the speed control will be lost.

Airbus has modes that are similar, whilst not the same.

V/S is rarely of any use above a few thousand feet.

An overspeed is a pretty minor event, especially if the aircraft is clean. Most types allow a few knots for a few seconds before anything needs to be looked at. I expect the issue will not be the overspeed as such, but rather the manual inputs made after (or causing) the autopilot disconnect. For crew to have been injured, I'd guess that there has been an abrupt pitch input.

 

[AviatorInsight]

VNAV PATH is the most common. In this case the aircraft will attempt to stay on the vertical path built in the FMC. It uses power as necessary to remain within a speed band, but once it hits idle, a steep path or wind change can cause the speed to drift outside of the range, in which case it will shift to VNAV SPEED. In that case it will hold on to the programmed speed, but will lose the path. It will recapture it if the opportunity arises. Selecting a hard speed on the MCP will also cause this mode shift.

In Boeing aircraft with a more sophisticated FMC/MCP that's correct, but VUE, and all the V** registered aircraft don't have a speed intervention mode. So if you start the descent in VNAV PTH, then it will remain in that mode until you physically select another mode, usually it'll be LVL CHG (quicker to hit on the MCP than to be heads down and select VNAV SPD, confirm, and execute) to open the speed window and get back on the path then re-engage VNAV.

That's one thing I've found with the B737 compared to the B777, lots more button pushing and management of the autopilot!

 

[jb747]

In Boeing aircraft with a more sophisticated FMC/MCP that's correct, but VUE, and all the V** registered aircraft don't have a speed intervention mode. So if you start the descent in VNAV PTH, then it will remain in that mode until you physically select another mode, usually it'll be LVL CHG (quicker to hit on the MCP than to be heads down and select VNAV SPD, confirm, and execute) to open the speed window and get back on the path then re-engage VNAV.

So..have I got this right? If your path steepens and the speed starts to increase...it won't eventually automatically transition to VNAV SPD? And, you can't intervene by putting a speed into the MCP window and forcing it to change to VNAV SPD?

 

[AviatorInsight]

So..have I got this right? If your path steepens and the speed starts to increase...it won't eventually automatically transition to VNAV SPD? And, you can't intervene by putting a speed into the MCP window and forcing it to change to VNAV SPD?

Yes that's correct. Our normal descent speed is to transition into 280kts. The company has an agreement with ATC that a speed excursion of 20kts is acceptable while on descent only. If we are given a max speed that flexibility no longer applies. So if I'm on descent in VNAV PTH I'll let it run to 300kts before I'll change modes to keep it on the path as long as possible.

Even in the new aircraft, I'll have to manually push the SPD INTV button next to the speed window to force the aircraft into VNAV SPD. It won't actually change modes automatically like it did in the B777 and I'm guessing same thing for the B767/B747?

 

[jb747]

Not the behaviour I expected in a 737-800, given that it's so much younger than either the 767 or 747. Of course, we could then talk Airbus...though I must admit that I've come to like the way the 380 does it.

Here's a bit of behaviour to watch out for. It's come and gone a number of times over the years...

You build a descent, which passes through a holding point (eg, Bindook). You expect that you will be held, and put in a "B" height at that point. So, profile descent, next waypoint has (say) B250 in the FMC. VNAV PATH. ATC clear you to FL250, which is put into the MCP.

You'd expect the aircraft to level off at FL250, as it shouldn't ever go through the MCP altitude. But, in this case, it ignores the MCP, and simply continues to follow the path.

 

[AviatorInsight]

Not the behaviour I expected in a 737-800, given that it's so much younger than either the 767 or 747. Of course, we could then talk Airbus...though I must admit that I've come to like the way the 380 does it.

Here's a bit of behaviour to watch out for. It's come and gone a number of times over the years...

You build a descent, which passes through a holding point (eg, Bindook). You expect that you will be held, and put in a "B" height at that point. So, profile descent, next waypoint has (say) B250 in the FMC. VNAV PATH. ATC clear you to FL250, which is put into the MCP.

You'd expect the aircraft to level off at FL250, as it shouldn't ever go through the MCP altitude. But, in this case, it ignores the MCP, and simply continues to follow the path.

Hmm that's an interesting scenario and I haven't come across that in holding just yet, although having said that, I always put 250A so when I exit the hold, it won't descend me until after the holding fix.

Also, you're quite correct in that it isn't a behaviour I expected transitioning onto the 737 either. It may be younger, but it's still operating as if it were 1960.

 

[jb747]

I guess that back in 1985 or so, Boeing were expecting the 757 to replace the 737. In retrospect, it's a pity that didn't happen...as they'll soon have to reinvent that particular wheel.

I discovered the FMC issue I mentioned back in the 90s on the 767. Once I'd worked out exactly how to repeat it, I went to see the technical people...and their initial reaction was 'b/s'. But, they passed it on to Boeing, and I was rung back within a few hours to tell me that they had been able to reproduce it in the 757/767/747 systems simulators. Don't remember if the 737 was mentioned. A red bulletin came out, and it disappeared in the next software update...only to return in the early mid 2000s, when I found it on the 747. So I got my second red bulletin. I guess the code was being written around, without being removed, so I've always wondered if it could make a comeback.

For the non pilots reading, holding patterns are one of the places where you can find a use for most of the vertical modes. In most cases you'll arrive at the holding fix in VNAV (managed - AB), but once in the pattern, FLCH (open descent - AB), and V/S start to have uses. Leaving the pattern, depending upon height and distance to run, any of the modes could well be selected.

 

[Happy Trails]

Any thoughts on this?
I'm surprised it's not made the mainstream news if it's as serious as it seems.

Incident: Emirates A388 at Moscow on Sep 10th 2017, go around from about 400 feet AGL 8nm before runway

An Emirates Airbus A380-800, registration A6-EEZ performing flight EK-131 from Dubai (United Arab Emirates) to Moscow Domodedovo (Russia), was positioning for an approach to Domodedovo's runway 14R about to intercept the extended runway center line about 8nm before the runway threshold when the aircraft descended to about 400 feet AGL, initiated a go around climbing straight ahead and crossing through the localizer to safe altitude. The aircraft subsequently positioned for another approach to runway 14R, aligned with the extended runway center line but did not initiate the final descent and joined the missed approach procedure as result. The aircraft positioned again for an approach to runway 14R and landed without further incident on runway 14R about 35 minutes after the first go around (from 400 feet AGL).

Position and Altitude data transmitted by the aircraft's transponder suggest the aircraft was tracking about 190 degrees magnetic when the aircraft initiated the go around at about 1000 feet MSL about 8nm before the runway threshold, which translates to about 400 feet AGL with the aerodrome elevation at 180 meters/592 feet MSL.

 

[jb747]

I'm surprised it's not made the mainstream news if it's as serious as it seems.

The ability of the mainstream news to pick the difference between real events, and trivia, is pretty limited.

There is a thread about this on pprune, with the normal quality range within the answers.

Common theories involve the use of QFE vs QNH altimetry (one is height above the airport, whilst the other is height above mean sea level), and the use of metres vs feet as the unit of measurement. Conversion between the two is fairly trivial (the aircraft will display metres if selected). Neither explains why you'd want to be at less 1000' at 8 miles from the runway, whilst still on the base leg.

The track and height from the first approach initially looks like they're tracking for a 5 mile intercept on the ILS (not a great idea in a 380 BTW). It's not too bad until about 2,000. After that they simply don't stop their descent, which is weird given that they aren't even lined up. The second time around, they don't even attempt the approach, so perhaps still changing undies. Third approach is normal, and from a more normal starting position.

I can't explain what I'm seeing based only on FR24, though it does look nasty.

 

[Berlin]

QF7 SYD-DFW also went off runway 25 while I was at the airport, which was the first time I'd personally seen an A380 do that.

Wow. I always wondered if the big bird would EVER take off from that runway. Impressive!

 

[pjm99au]

Morning all. One of my twins is starting the journey of realising his dream of becoming a pilot having been accepted to undertake initial aptitude testing under the Jetstar cadet pilot program.

From what we can see the initial testing comprises assessment for things like IQ, maths, physics, psychometric and coordination. An interview process follows if he successfully gets through the initial testing

Just wondering if anyone has experience of the testing process and what sort of things he can expect

Thanks in anticipation

 

[jb747]

Wow. I always wondered if the big bird would EVER take off from that runway. Impressive!

The A380 has better take off performance than the 747. The shorter runways in Oz are rarely used, because on most flights it's going such a long way, that the weights are right up near the max. In nil wind (and Sydney 25), you could go at up to 534 tonnes, whilst a headwind of 20 knots would get you to 560 tonnes.

We will take the crosswind on a long runway in preference though, as it is much kinder to the engines, and we have more options on long runways.

 

[jb747]

Morning all. One of my twins is starting the journey of realising his dream of becoming a pilot having been accepted to undertake initial aptitude testing under the Jetstar cadet pilot program.

From what we can see the initial testing comprises assessment for things like IQ, maths, physics, psychometric and coordination. An interview process follows if he successfully gets through the initial testing

Just wondering if anyone has experience of the testing process and what sort of things he can expect

Hopefully one of the younger guys might be able to give you some idea. For me, that sort of testing is so far in the past, that I barely remember even doing it.

There is discussion about this on pprune, so you might be able to find some information there, though there also a lot of 'noise'.

Good luck.

 

[AviatorInsight]

Morning all. One of my twins is starting the journey of realising his dream of becoming a pilot having been accepted to undertake initial aptitude testing under the Jetstar cadet pilot program.

From what we can see the initial testing comprises assessment for things like IQ, maths, physics, psychometric and coordination. An interview process follows if he successfully gets through the initial testing

Just wondering if anyone has experience of the testing process and what sort of things he can expect

Thanks in anticipation

That's excellent!

The testing can be quite intimidating at first but with practice will increase their chances at success. The test is similar to the ADAPT system. Google it and you'll find a bit of info about it. You can pay to do some practice tests, but you can also go through SHL and they have a similar sort of thing also.

Basically the questions start out easy, then get harder as you progress. You want a comprise between accuracy and time to a question. The psychometric gets tedious with about 400 questions to evaluate your profile. They will ask the same question in a different way numerous times to see if you're trying to answer what you think they want you to be or how you actually are. If successful they will subtly do this in the interview too.

Good luck!

 

[Quickstatus]

Regional Express Delays/Cancellations
speculative question at the end of the post related to today's radar issue at SYD...