[audioholic]

Though I have no flying experience other than regular simming, why is it that flaps arent avoided during crosswinds? Wont it give the aircraft better stability since the wing area will be lesser? Agreed it will reduce lift but perhaps a faster landing would be okay compared to losing stability during landing?

@Rakeshnair, on what basis do you say that the A320 is preferred? Is it in terms of number of sales, or it because of its commonness in our country? If its the latter then IMHO its due to carriers like IndiGo, the newly launched AirAsia etc trying to maintain a uniform fleet and avoiding different types of aircraft in their fleet, since it will help in easier maintenance.

The Airbus v/s Boeing debate is quite a common discussion everywhere. One major difference being the A320 is fly by wire whereas the 737 is not. Not sure if that itself categorises it as advanced, since all the actions of the pilot is mediated by the onboard computers.

[Jeroen]

Originally Posted by audioholic

Though I have no flying experience other than regular simming, why is it that flaps arent avoided during crosswinds? Wont it give the aircraft better stability since the wing area will be lesser? Agreed it will reduce lift but perhaps a faster landing would be okay compared to losing stability during landing?

The Airbus v/s Boeing debate is quite a common discussion everywhere. .

Flaps will improve lift charasteric, but at the expense of introducing additional drag. . Essentially it reduces the speed at which an aircraft can be flown safely. It also allows for a steeper approach to the runway.

In cross wind situation the windward side of the plane/wing will produce more lift and drag than the lee side of the plane/wing. So the pilot will need to compensate for roll, yaw and pitch changes.

These effects depend heavily on the plane and wing design amongst others.

I can not speak for the big commercial planes, other than the Boeing 747 see below, but on smaller planes, landing with reduced flap setting for crosswind landings is a normal practice.

The last time I flew a small plane I had to reduce flap settings for this reason, see here: http://www.india.jeroendorrestein.co.../Santa_Fe.html

Of course, a lower flap setting, means a higher landing speed and thus you need a longer runway. So you do need to take that into consideration.

Small planes such as Cessna's etc are perfectly capable of landing with no flaps at all. You just need to take into account the higher landing speed. In theory you would also not be able to descent as steeply, but again that tends to be not an issues for these planes at all. On single engine plane, when flying VFR, you typically try to come in a little high always, just in case your engine coinks out and you have to glide in the last few hundred meters.

When you're flying IFR and a subsequent instrument landing, you might not have that option, or at least it's a little more tricky to do.

On small planes being a little high and fast is easily remified by introducing forward slip. Something you wouldn't want to do with a big airliner.

Also cross landing techniques between these small and large planes tend to vary. 10 knot crosswind in your little Cessna C150 is quite a lot already, whereas for a big commercial airliner it's probably not a lot at all. techniques vary as well. Look up cross wind landing on youtube and you'll find dozens of video's and you will notice different techniques.

In a crosswind most planes come in at a crab angle. So the nose of the plane is not pointing in the same heading as the runway heading, but at an angle. In order to land the plane needs to be de-crabbed in some point of the landing. Some (larger) planes actually do land in a crab configuration and will only start alligning once the main gear hit the runway. The big issue for landing in a crab is the additional strain it puts on the landing gear. Some planes are designed and certified to allow for a certain crab angle. A few planes compensate for the crab angle by being able to rotate their landing gear the exact same amount of crab in the different direction (E.g. Boeing B52)

On a small plane the most common technique is at about 500 feet above ground to lower the wing that is in the wind. To compensate for that you need to introduce opposite rudder. Both will introduce extra drag, so you need to watch your airspeed and throttle settings carefully. In essence with the rudder you lign up the nose of the aircraft on the centreline and with dipping the wing you allign the aircraft on the centreline.

Some pilots will "kick out the grab" just before touchdown.

Either way, it means that the wing in the wind is always down from the level position, the stronger the crosswind the lower the wing needs to be to keep the plane alligned with the runway centre line. Obviously at some point you will have the wing touching the ground. Again, search on youtube for some telling examples. It also means that on a crosswind landing you typically land on one of the two main landing gears first. The one that's in the wind.

But if anything Crosswind landings seperate the real pilots from the crowd on any plane big or small. I loved doing them, but it took endless training. For me it was very much a safety issue. The more crosswind you can handle competently the more airstrip are available to you in case of an emergency!

Auto pilots in combination with Auto throttle system are capable of conducting safe crosswind landing right up to the certified cross wind speed.

On small planes there is no certified cross wind speed (at least not in the USA, under FAA rules). There is only a safe demonstrated cross wind speed.

On some large airliners, (Eg. Boeing 747-400) the standard operating procedure gives pilots two different flap setting 25 and 30. For all of the above and of course there is also some effect on brake wear. Higher landing speed means more brake wear ultemately.

On the differences between Airbus and Boeing; I have no idea if there are favourites. I just dont have the data. But as pointed out there are material differences in how these plane operate. On what's better the jury is still out on that.

Jeroen

[Jeroen]

As I stated earlier, lots of youtube videos out there about crosswind.

Have a look at this one and compare the first landing with the second one. You will see the first one lands with full crab and the second one kicks out the crab angle just before touching down.

https://www.youtube.com/watch?v=la-hSjKP2TU

Here's an interesting instructional video on landing with crosswind:

https://www.youtube.com/watch?v=mj5w6UEW7eM

enjoy, Jeroen

[audioholic]

Originally Posted by Jeroen

As I stated earlier, lots of Youtube videos out there about crosswind.

Have a look at this one and compare the first landing with the second one. You will see the first one lands with full crab and the second one kicks out the crab angle just before touching down.

I have seen most of the crosswind landing videos and its hair rising to watch the way the pilots control the plane. That itself led to my doubt since during the final 100 ft or so, the plane oscillates and the pilots have to constantly correct their control and compensate for the drift. Thats when I felt perhaps the oscillations may reduce if flap extension is reduced to some extent.

But yes, your explanation does answer the question well. Increased landing speeds may be unsafe compared to a rough touchdown.

I have a question WRT the Microsoft FS. Over the last few months I've managed to learn the basics, and I can use the various equipment and fly a commercial plane(thanks to autopilot to some extent ). I have managed to align and land the plane without sending it off the runway or anything. But one problem I face is most of the times I tend to bounce the plane before it settles onto the surface of the runway. I land at the prescribed speed, flaps and power is at idle. Once the rear gear is about to touch the surface I flare up. But once it touches down, it clearly bounces off, thus making me bring down the nose and sometimes breaking the front gear. Am I too fast or are the flaps too outward? I am landing at the specified speeds in any plane.

[Jeroen]

Originally Posted by audioholic

I have managed to align and land the plane without sending it off the runway or anything. But one problem I face is most of the times I tend to bounce the plane before it settles onto the surface of the runway. I land at the prescribed speed, flaps and power is at idle. Once the rear gear is about to touch the surface I flare up. But once it touches down, it clearly bounces off, thus making me bring down the nose and sometimes breaking the front gear. Am I too fast or are the flaps too outward? I am landing at the specified speeds in any plane.

Its a bit difficult to come to some sort of conclusion without actually seeing what happens, but here are a few things you might want to check:

Speed, approach and flare technique.

I assume you know how to figure out the correct speed and flaps settings? If your speed is too high, it's always going to be tricky at best. How do you know you have the correct landing speed/flap settings for the landing weight?

But if your speed is correct for the weight and the flap settings I would suspect you might "flare" a little bit to enthusiastically. Or your whole approach might be to steep. So basically at touch down your vertical speed is too high. Have you managed to fly an approach using a glide slope? that will help you get a good stable approach at the correct angle and makes the flare easier as well.

On most commercial planes the flare is a pretty subtle maneuver. If you bounce you can do either of two things:

Go around, or keep the nose up. But you should never force the nose down. That will make things worse, you could end up ballooning over the runway and breaking the nose gear. Happens for real as well. Several youtube video's out there on this as well. Have a look:

https://www.youtube.com/watch?v=QlaRppxPQPY

If you bounce a bit and you have sufficient runway left, hold the plane in the normal flare position and just wait for it to settle down on the runway. I can't really remember anymore on how well MS simulates ground effect, but even so.

Here is another suggestion. Put the autopilot and auto throttle on, find yourself a good ILS approach and learn how to execute a complete auto landing. Simulating auto landings is a great way of getting a feeling for how things should look like, speed, flare, roll out etc.

There is a difference on how you land small planes (e.g. Cessna, Cirrus) and large commercial planes.

Small planes land because you fly them into ground effect and bleed of airspeed until the wings stall and the airplanes literally stops flying and settles on the runway. Check out some of the youtube video's and you will hear the stall warning going. see/hear

https://www.youtube.com/watch?v=cqU6NkB82gg

The larger commercial airplanes you don't stall during landing, you actually "fly" them into the runway. The ground effect cushions it, sometimes quite considerable.

There are also tonnes of MS video's out on youtube. You might be able to find one of the plane you're flying and see how how its done.

Good luck!

Jeroen

[Jeroen]

Not sure if there was a seperate thread for the Asiana crash in San Francisco, if so, I cant find it.

Here are the latest finding of the NTSB and they put the blame squarly on the pilot(s).


http://www.sfgate.com/bayarea/articl...081.php#page-1

Jeroen

[ameaa]

Originally Posted by Jeroen

Not sure if there was a seperate thread for the Asiana crash in San Francisco, if so, I cant find it.

Here are the latest finding of the NTSB and they put the blame squarly on the pilot(s).


http://www.sfgate.com/bayarea/articl...081.php#page-1

Jeroen

Report mentions pilot moving the throttle to idle to align with glide slope and was expecting the auto throttle to maintain the approach speed. Does the system work like this? I believe a manual override will cutt off the auto system. Also won't the crew get an aural warning when the aircraft approaches stall speed? It looks something similar to Turkish 737 crash recently.

Thanks, Ajith

[Jeroen]

Originally Posted by ameaa

Report mentions pilot moving the throttle to idle to align with glide slope and was expecting the auto throttle to maintain the approach speed. Does the system work like this? I believe a manual override will cutt off the auto system. Also won't the crew get an aural warning when the aircraft approaches stall speed? It looks something similar to Turkish 737 crash recently.

Thanks, Ajith

It's a bit more complicated then that. There are two autosystems that control speed. Its the autopilot that controls it through pitch and there is the autothrottle that controls it through engine thrust. Both have several different mode and interact with one another.

In this case the pilot made the wrong choice and that meant the autothrottle would not control the airspeed.

I'm not sure which recent Turkish 737 you are referring to. There was A Turkish plane crash at Amsterdam airport several years ago. Although the circumstances were very different, what was similar to this crash was that the crew failed to properly monitor the system and take positive action when they saw the plane was getting low and slow on the glide path.

Jeroen

[yaniv14]

Excellent thread, learnt a lot and cleared a lot of doubts.

Thanks for sharing your experiences.

[akshay380]

What is the use of red marked object? I have always wondered about it.

[audioholic]

Originally Posted by akshay380

What is the use of red marked object? I have always wondered about it.
Attachment 1254427

IIRC that is the housing for the driving mechanism of the flaps.I had the same doubt sometime and I remember reading about it.

[A350XWB]

Originally Posted by akshay380

What is the use of red marked object? I have always wondered about it.

Those are flap track fairings. The flap extension and retraction mechanism sits inside those. The covering is made in that shape for streamlining the airflow.

[Jeroen]

For those of you who are interested in some of the detailled aspects of aviation, the Dutch Safety Board just published a report on so called false glide slopes. These false slopes were a known phenomena, however, they investigated a recent incident in which the autopilot appeared to be receiving a reverse ILS signal.

The Dutch Safety Board has identified a dangerous response of the autopilot to the instrument landing system (ILS): aircraft landing on the autopilot may receive a reversed signal from the ILS. Instead of the expected descent, the nose of the aircraft comes up unexpectedly causing the aircraft to climb. The resulting loss of speed may cause the aircraft to stall, in which case the wings lose so much of their lift that the aircraft risks falling from the sky.

The 3-degree glide slope is prescribed to ensure a stable and safe landing. The instrument landing system will guide the aircraft to the runway along this route. However, if the aircraft approaches from a higher than usual altitude and aims to capture the 3-degree glide slope from above, it risks intercepting a ‘false’ glide slope. This term is used in aviation to denote the non-prescribed 6 and 9-degree glide slopes. The ILS may send a reversed signal to the aircraft when it crosses a false glide slope.

http://www.onderzoeksraad.nl/en/onde...se-glide-slope

Jeroen

[audioholic]

Dangerous thing but I dont understand how the 6deg and 9deg glideslope are created. Can anyone explain that part? I thought just like the localiser, the signal will be lost if one tries to capture the glideslope from above it.

Edit: Google helped me out with it

Guess the system must be made foolproof to ensure the correct glideslope is captured. I assumed the transmitting antenna for the glideslope was highly directional with no significant sidelobes. In one picture I saw they portrayed strong sidelobes :O . Cant the glidescope too have an identification code which can be demorphed only if the 150hz and 90hz signals are properly captured? Just like the ILS code for each runway even the GS can get a code which must be garbled if the GS is captured in the wrong way.

[Jeroen]

Originally Posted by audioholic

Guess the system must be made foolproof to ensure the correct glideslope is captured. I assumed the transmitting antenna for the glideslope was highly directional with no significant sidelobes. In one picture I saw they portrayed strong sidelobes :O . Cant the glidescope too have an identification code which can be demorphed only if the 150hz and 90hz signals are properly captured? Just like the ILS code for each runway even the GS can get a code which must be garbled if the GS is captured in the wrong way.

The industry has known about the false lobe for quite a while. I checked on Prune.org and there you will find messages going back as far as 2007. Several incident and accidents have been related.

Pilots (should) are trained and their companies SOP should have specific instruction on how to fly the ILS. You can't just assume it's ok.

So you are taught to do multiple altitude/DME checks, cross checking altitude agains FMS threshold distance, checking ground speed and rate of descent, cross checking radio altitude and barometric altitude etc.

So there are a lot of things you can and should be checking whilst on the ILS glide path. But then again, this is a flight regime with a very high work load already. Never the less, any instrument rated pilot (should) know how to do this.

Capturing the glide slope from below is the preferred method, rather then from above as you could 'catch' one of the other two lobes. Unfortunately, due to noise reduction restrictions and or ATC instruction you might not have the option to capture from below. If you are capturing from above, you need to extra cautious.

The ILS signal is influenced by many other parameters as well. A lot of that is taken into consideration during the design of an ILS approach. Eg. nearby buildings, power cables etc. Even on the taxiway there are different hold lines for ILS and non ILS operations.

What the Dutch safety board found, and that was the new bit, is that the autopilot systems gets revered signals if they capture one of the false lobes, so instead of commanding the plane downards, it actually pitches nose up. Which is never a good thing when you're low and slow!

Interestingly when I was reading through the various PRUNE messages from years ago, it appears that it was known that not only the false lobes exist but also that there is signal reversing. But it seems, until this recent event that prompted the Dutch Safety Board investigation that was never investigated in depth, although with hindsight they found several similar incident in both Europe and the USA.

Jeroen