Ask The Pilot

[markis10]

Hey jb !

I have been flying long haul back and forth between Buenos Aires and Madrid on the A340-600 (not a big fan?) with Iberia. We had some bad weather when we ran into extremely thick cloud that lasted for nearly an hour, what type of cloud is this and what is the reason that clouds cause turbulence? What is the worse type of cloud and weather conditions for an aircraft? Another thing I noticed, we would be flying through cloud experiencing bad turbulence but when I looked out the window I noticed clear sky above, is there a reason a pilot wouldn't choose to increase the altitude to stay out of the clouds? Do you need permission to change altitude or if its more calm the captain can make a decision assuming there is no other air traffic up there? I think we were only cruising at 34,000 feet which is quite low in my experience.

Sounds like you were in convective turbulence of indicated by coughulus clouds. As for not being able to increase altitude, there could be a number of reasons for it such as other aircraft traffic and generally speaking pilots require permission to change altitude at all times unless they are given an altitude block or range of levels between two limits that they can move between, although at cruise this is not often done owing to the limited number of levels that exist in the first place.

 

[harvyk]

At top of descent does ATC automatically grant lower altitudes (knowing the pilots flight plan) or does the pilots need to actually request a descent to a certain altitude from ATC?

 

[markis10]

At top of descent does ATC automatically grant lower altitudes (knowing the pilots flight plan) or does the pilots need to actually request a descent to a certain altitude from ATC?

The pilot needs to request descent as its not indicated on a civil flight plan (it is on military ones if they involve a LJR or low jet route or its a P3 going tactical at 200agl with 2 turning and burning instead of 4).

I was watching an America West 732 going MEL CBR during the pilots strike one day and he was 15 miles south of Canberra still at FL310, at which time I dropped a subtle hint "Cactus 123, confirm approaching top of descent ?" . He dropped almost as quick as the F18 climbed ex CBR that I gave the requirement to be at FL290 within 2 DME of CBR (ie go ballistic).

 

[harvyk]

Excellent, so MS Flight Sim gets it completely wrong...

 

[jb747]

I have been flying long haul back and forth between Buenos Aires and Madrid on the A340-600 (not a big fan?) with Iberia. We had some bad weather when we ran into extremely thick cloud that lasted for nearly an hour, what type of cloud is this and what is the reason that clouds cause turbulence? What is the worse type of cloud and weather conditions for an aircraft?

Watch the clouds, especially the big ones, from the ground, and you'll see that they pretty well always have quite a bit of vertical motion in them. To an aircraft, any different motion in the air (compared to the bit that it's currently in) is more or less a pot hole. BTW, air pockets, so beloved of the newspapers, do not exist.

As you mention lightning, it was quite likely that the aircraft was traversing a storm front. These can extend for many hundreds of miles, and contain dozens of individual storm cells.

Another thing I noticed, we would be flying through cloud experiencing bad turbulence but when I looked out the window I noticed clear sky above, is there a reason a pilot wouldn't choose to increase the altitude to stay out of the clouds? Do you need permission to change altitude or if its more calm the captain can make a decision assuming there is no other air traffic up there? I think we were only cruising at 34,000 feet which is quite low in my experience.

Any time that there is any form of interface in the atmosphere, whether it be the edge of cloud, or a temperature or wind change, there will be some level of turbulence. So, sitting just on the tops of the cloud is likely to be a bit bumpy. The airspace around the world is very rigidly controlled, and you can't just decide to climb or descend to get out of a few bumps (well, you can if you declare an emergency first, but bumps don't qualify). Flying at FL340 sounds like an RVSM even height, which means that the next level available is FL360. If someone already has that level (generally within 10 minutes in either direction), then you can't go there. As FL340 was lower than you'd previously experienced, that might indicate that he was being held low by other traffic. But, performance often limits options too. Aircraft are often cruising within a couple of thousand feet of their maximum altitude, so going higher, especially in any turbulence, simply may not be an option. Descending into the cloud will often bring some relief..but not always.

Also had an amazing few of huge lightning storms going off just below us, the plane was weaving left and right trying to avoid all the lightning hotspots, pretty amazing seeing the power of nature from that perspective. I was very happy the captain chose not to take us through any of the lightning areas, he did a great job avoiding them. Is the primary tool the radar? What range is it effective at in predicting weather and turbulence? Thanks

Having lightning going off underneath you isn't all that desirable, but it's also, at times, unavoidable. If you're going past thunderstorms, a ten mile berth is about the minimum that you'll try for...though sometimes the gaps just aren't that big. If there is space, the more margin the better.

The radar systems basically show moisture. The more moisture, the more dense the cloud, and presumably, the nastier. The radar systems do incorporate a doppler function, so that they can measure movement, and attempt to predict areas of severe turbulence, but that requires quite high definition, and so is quite short range (about 40 miles). Normally I'll start to manoeuvre when about 60-80 miles from any weather. The radar actually shows returns hundreds of miles away (the radar horizon in miles, is roughly 1.23*(square root of aircraft height in feet)), but the ability to discriminate between adjacent targets deteriorates with range (it's actually an angle...you can't discriminate between targets less than a beam width apart).

The display shows up to us in various colours...predictably green should be ok, yellow less so, and red you should keep out of. Magenta is a total no go. But, like any system, what sounds quite simple will actually need some level of interpretation. For instance heavy rain, but not associated with any nasty clouds, will still show up as red, even though flying in it simply gives the aircraft a wash.

Lightning strikes...well they happen. Quite regularly in fact. Normally they do virtually nothing to the aircraft. The engineers can sometimes find scorch marks on the aircraft, often on the stainless steel near the engines. It will be interesting to see how the new construction techniques handle lightning, but it will have been tested extensively. Thunder from the strike is very, very loud, and scares the bejeezus out of people.

Most likely place for a strike to happen is when near an airport...that's when your tracking options are most constrained.

 

[jb747]

Probably about 50% of the time, we request descent. Within Australia, standard speeds have been agreed between the airlines and ATC, with the result that for a given type, the descent points don't vary much from any given altitude. Going into London, you normally get a conditional clearance on first contact with them. They give you a STAR (a standard arrival, normally via Lambourne), with a requirement to reach one of the waypoints at a certain altitude...you descend when ready, to ensure you make that height. Of course, they see this many times every day, so normally you get the clearance within a minute of needing to descend anyway.

LA and Frankfurt descend you very early, to fit in with their traffic flows. Going to Singapore, the actual descent points are often in adjacent airspace (Indonesian or Malaysian), with the result that you quite regularly get 'hung up' for a few miles. But, it doesn't matter, as the radar vectoring into Singapore has become so extensive as to make descent planning a bit of a joke.

 

[jb747]

The ATSB has released their report on the Qantas A333 incident near Learmouth in Oct 2008

Accident: Qantas A333 near Learmonth on Oct 7th 2008, sudden inflight upset injures 74 people on board

From a pilot's point of view, is this a design fault ?

I haven't read the report yet (that will give me something to do in London in the next couple of days). I know the Captain well, and have spoken to him about this incident.

The problem with any aircraft or system is that the engineers hopefully build it to cover any event with odds that make it even vaguely likely to happen. But, as we've seen a couple of times recently, sometimes the odds they work out (or perhaps just pluck out of thin air) are often dramatically worse in the real world than they are in the rarified air of an engineering conference room. And, sometimes, they just don't even consider something, and so don't cater for it at all (oxygen bottles come to mind there).

I suspect that it's fair to say that at least some Airbus pilots wish that there was a big red switch in the aircraft that gave instant access to direct law (I've been told that the RAAF A330 tankers have this). That has the effect of getting rid of the computers. On the other hand, it could be argued that access to a lower law, and not being able to fly it, was what caused the AF 330 to crash.

 

[jb747]

A rundown on another sim exercise.

Start in Dubai. Two circuits, one for each pilot.

F/O takes off, flies a standard departure, and then that joins up to a VOR approach back to the same runway. Go around off the approach. Hand over to Captain, who then flies the same approach and lands, but this time with no glide slope guidance (PAPI or ILS g/s). F/O takes off, radar vectors into rising terrain, GPWS pull up warning. (Response is A/P off, FULL back stick and hold it there, TOGA, speed brakes down). Captain does same. Both then do some flying on the standby instrumentation (all of the big screens turned off).

Low vis training, with both take offs and landings at the minima. Engine failure and abort on first take off. Later an engine failure and continue. Three engine Cat III approach. Go around, autopilot disconnects as the go around is started. (This is interesting in the Airbus, because it's FBW, it does not pitch up with application of GA power, and needs a definite pull to get the go around attitude. 767/747, have very strong pitch couple, and normally you are pushing forward to stop the nose coming up too far.) Back into 3 engine clean up...weather improves to Cat I, and fly a manual 3 engine ILS approach.

Aircraft now jumped to a spot about 150 miles from Dubai, and in the cruise. ECAM cargo door message, followed almost immediately by explosive decompression (!). #3 engine impacted by FOD and fails with severe damage. Go to Dubai again. Another go around, followed by failure of #4 engine. Two engine landing. Go home.

Added....sometimes there's a couple of minutes spare, and you can look at something that takes your fancy. This time we turned off all of the primary flight control computers to have a look at the way the system degraded. Didn't have time to land off it, but it left us with a perfectly flyable aircraft, albeit one without any automatics. Direct law.

 

[NM]

Another challenging day at the office.

Aircraft now jumped to a spot about 150 miles from Dubai, and in the cruise. ECAM cargo door message, followed almost immediately by explosive decompression (!). #3 engine impacted by FOD and fails with severe damage. Go to Dubai again. Another go around, followed by failure of #4 engine. Two engine landing. Go home.

Loss of #3 and #4 would obviously create significant asymmetric thrust. Is the asymmetry handled by the computers and you just fly normally with reduced maximum power available, or do you need to compensate for the asymmetry with trim and control stick/rudder inputs as you would in a non-FBW aircraft like the 744 in a similar multi-engine loss situation?

 

[jb747]

Loss of #3 and #4 would obviously create significant asymmetric thrust. Is the asymmetry handled by the computers and you just fly normally with reduced maximum power available, or do you need to compensate for the asymmetry with trim and control stick/rudder inputs as you would in a non-FBW aircraft like the 744 in a similar multi-engine loss situation?

Really much the same as the 747. The autopilot can handle it if the rudder trim is under control when you engage it. The lack of power means that you need to be careful of just how/when you configure it. If the autopilot is already engaged, it won't drop out (neither did the 747). Unlike the 747, loss of two engines (on the same side) will also mean loss of one of the hydraulic systems, which means that the gear has be extended via gravity. And it also means that you won't be able to retract it all if you need to. The approach is flown as much as possible with the autopilot engaged...we try to leave it in until roughly 200'. Rudder trim is removed immediately thereafter, so make sure you have that under control, as it's too late to fix it if you don't.

Procedurally it's more complex than the 747, but on the bonus side, it has enough power to go around down to about 500', whereas the jumbo commits you much earlier.

 

[Tortuga]

Any time that there is any form of interface in the atmosphere, whether it be the edge of cloud, or a temperature or wind change, there will be some level of turbulence. So, sitting just on the tops of the cloud is likely to be a bit bumpy. The airspace around the world is very rigidly controlled, and you can't just decide to climb or descend to get out of a few bumps (well, you can if you declare an emergency first, but bumps don't qualify). Flying at FL340 sounds like an RVSM even height, which means that the next level available is FL360. If someone already has that level (generally within 10 minutes in either direction), then you can't go there. As FL340 was lower than you'd previously experienced, that might indicate that he was being held low by other traffic. But, performance often limits options too. Aircraft are often cruising within a couple of thousand feet of their maximum altitude, so going higher, especially in any turbulence, simply may not be an option. Descending into the cloud will often bring some relief..but not always.
.

Thanks for the detailed response JB! I think it must have been due to air traffic - I noticed at least one other airline flying to the same destination that took off 10 minutes before us. Also had an aircraft flying to Rio De Janeiro around the same time which I assume follows a pretty similar flight path to us over the Atlantic. How do they decide who gets priority to fly in the "clearer" airspace? Also wondered how priority is given when there is congestion at an airport to different airlines by ATC - does the flight which is the most delayed get priority over a flight that could take off on time? Does nationalistic pride come into it? EG. Iberia gets better treatment in Spain over American Airlines?

Another question, I noticed that during bad turbulence the plane was getting tossed around to the left and right (eg. left side wings would point below the horizon level, right side above) - does the auto pilot have a feature that attempts to keep the plane level during these times by adjusting for these sudden movements?

 

[jb747]

Thanks for the detailed response JB! I think it must have been due to air traffic - I noticed at least one other airline flying to the same destination that took off 10 minutes before us. Also had an aircraft flying to Rio De Janeiro around the same time which I assume follows a pretty similar flight path to us over the Atlantic. How do they decide who gets priority to fly in the "clearer" airspace? Also wondered how priority is given when there is congestion at an airport to different airlines by ATC - does the flight which is the most delayed get priority over a flight that could take off on time? Does nationalistic pride come into it? EG. Iberia gets better treatment in Spain over American Airlines?

It should just be 'first in, best dressed', and it normally is.

So, whilst the queue should be just that, a queue, it's quite noticeable at times (and particular places) that some people are very good at jumping in.

Another question, I noticed that during bad turbulence the plane was getting tossed around to the left and right (eg. left side wings would point below the horizon level, right side above) - does the auto pilot have a feature that attempts to keep the plane level during these times by adjusting for these sudden movements?

The autopilot reacts to any displacement, by putting the aircraft back to where it was beforehand. The autopilots have many modes, and normally they are much more complex than just holding an attitude. So, whilst it will target going back to where it was, it will also adjust that target attitude to ensure that it achieves the performance appropriate to the mode.

But, in the AB, there are a couple of other systems at play that can affect the ride in the cabin. The rudder will automatically be putting in small inputs to damp out any yaw, which you may feel as sudden lateral motions. The wings too, will be active with two load alleviation functions (by symmetrical use of ailerons and spoilers).

 

[markis10]

It should just be 'first in, best dressed', and it normally is.

So, whilst the queue should be just that, a queue, it's quite noticeable at times (and particular places) that some people are very good at jumping in.
.

It does vary by country and airport but often there is a set list of priorities mandated by law, in Australia for landing:

1. An aircraft in an emergency including unlawful interference
2. A multi engine aircraft with an engine failure not considered to be covered by item 1 or a SAR phase.
3. An Aircraft that has suffered a radio failure
4. An aircraft that has declared a Mercy Flight
5. An aircraft engaged in SAR/MED1/HOSP/FFR (Flood Fire Relief) airwork
6. An aircraft operating under the call sign Polair Red or Fedpol Red
7. An aircraft carrying a head of state or Julia or the gov gen

At Sydney the following then applies:

RPT
Non RPT heavier than a BAE146
Military Flights not on training
State Governors or Premiers
Med 2 flights.

 

[jb747]

I was just thinking of airlines...one would expect them all to be treated equally, but it doesn't always seem that way. Of course, it could be argued that I don't see all of the picture, and that's true. But, it's difficult to understand how some of the things we see play out. It's especially evident on the ground...

I should add that I'm thinking of one particular place, and it isn't in Oz.

 

[markis10]

I was just thinking of airlines...one would expect them all to be treated equally, but it doesn't always seem that way. Of course, it could be argued that I don't see all of the picture, and that's true. But, it's difficult to understand how some of the things we see play out. It's especially evident on the ground...

I should add that I'm thinking of one particular place, and it isn't in Oz.

There is certainly no preference as far as airlines go, with priority given based on ETA into the arrivals stack, having said that there use to be an impression cast by some pilots that they should have priority regardless as SYD was their home base , this was 15 years ago mind you!

 

[jb747]

There is certainly no preference as far as airlines go, with priority given based on ETA into the arrivals stack

The Sydney arrivals system has always bemused most of us. I vividly recall being radar vectored all over the place so that a 737 from the opposition (which was higher than me, about 20 miles behind, and .05 slower) could get in ahead. Presumably I'd overtaken him after the point at which the sequencing was fixed, but it was a wasteful, and inflexible, exercise anyway.

....having said that there use to be an impression cast by some pilots that they should have priority regardless as SYD was their home base , this was 15 years ago mind you!

Perhaps we'd see that as balancing the books.

 

[harvyk]

How much latitude does a pilot have (outside of an emergency situation) to tell ATC that they can't do something? Has the situation ever arisen?

 

[jb747]

How much latitude does a pilot have (outside of an emergency situation) to tell ATC that they can't do something? Has the situation ever arisen?

Well, if you can't do it, then that's the end of the discussion. ATC sometimes comes up with requirements to reach altitudes by a certain spot...especially when simultaneously combined with a requirement to slow down. Just tell them you're unable, and they'll come up with a new plan.

But, you need to be on the same wavelength as ATC. Even in an emergency, you have to be aware that your actions may impinge upon other aircraft, so if at all possible, get ATC into the picture ASAP. Of course, if you've just depressurised, and they tell you to maintain altitude, then that might be the end of the relationship. Actually ATC are normally extremely good at helping out when needed.

Mostly ATC have a very good knowledge of what the aircraft (and crews) can do, and when they ask for something outside of that, it's just as likely a simple mistake, easily fixed by a quick radio call.

The airlines and ATC do regularly talk, in an attempt to minimise any confusion. An example from a few years ago, we had feedback from them that our 767 crews were extremely variable in just how flexible they were. A closer look showed that the crews arriving after all night international flights behaved quite differently to those on short sector days. They had, after all, been up all night, and were simply being conservative to suit. Of course, that wasn't necessarily obvious to ATC, as they may have done the all night sector to Melbourne, or Brisbane, before taking a domestic flight number to Sydney.

Back closer to your original question...about the only regular occasion on which we give Australian ATC a no go, is when they assign short, out of wind runways to large aircraft. And that's because ATC aren't making the decisions, but governments have stuck their fingers into the pie. Flying a 747 (or a 767 for that matter), why on earth would I accept landing on a 2200 metre runway, when there is a perfectly nice 4000 metre one sitting there? Same goes for 16L in Sydney...there is no logic to landing a 767 on that runway, whilst a Dash 8 lands on 16R (twice as long). It might fit a noise sharing, or convenience, or some other profile, but it massively increases the risk that I take, so therefore, I don't.

 

[jb747]

If anyone is travelling over the next couple of days....

QF9 Melbourne - Singapore 23 Dec
QF9 Singapore - London 24 Dec
QF32 London - Singapore 27 Dec
QF32 Singapore - Sydney 30 Dec

 

[straitman]

If anyone is travelling over the next couple of days....

QF9 Melbourne - Singapore 23 Dec
QF9 Singapore - London 24 Dec
QF32 London - Singapore 27 Dec
QF32 Singapore - Sydney 30 Dec

How about Jan dates JB?