Earning Your Pay

[Kip Powick]

Tubes, Torque, and Wind..

Watch in FULL SCREEN

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

[J.O.]

I'm not sure which video you were watching but in fact it was Aer Lingus and Emirates who got it right. The rest had the flight deck sitting over the centreline as they came over the threshold, meaning that the wheels were well right of it when the touched down.

[W5]

Looks like JAT Airways

[mrlupin]

Great video Kip.

A question for you commercial pilots:

Can you side slip these big birds on approach (or any other time) or is that a technique reserved to the smaller birds?

[J.O.]

You "can", but you shouldn't. It's quite dangerous in a swept wing aircraft.

[HST]

A question for you commercial pilots:

Can you side slip these big birds on approach (or any other time) or is that a technique reserved to the smaller birds?

You "can", but you shouldn't. It's quite dangerous in a swept wing aircraft.

Side-slipping a swept-wing aircraft can have undesirable consequences.

The answer mrlupin is yes you can sideslip a wide body Boeing (see below) and Airbus. The Sideslip method is a technique shown in both operators manuals (although not an Airbus "recommended" procedure). http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-LAND-SEQ05.pdf

To say, in general, side slipping is dangerous in swept wing aircraft isn't accurate IMHO. As with any aircraft, maneuvering outside the operators recommended limits is dangerous. In fact, the autopilot will sideslip in a crosswind autoland.

*** Sideslip only (zero crab) landings are not recommended with crosswind

components in excess of 31 knots.

[canadairguy]

Do Airbus or Boeing publish a max crosswind limitation for any of their types or merely a max demonstrated crosswind?

[Southshore]

While not a "big bird" as somebody put it, the BAe-146 was a fabulous cross wind machine. I'm guessing it's because it had an anhedral wing. The bigger the bumps and stronger the wind, the more stable it got, to my feeling. Good fun, I'll tell ya that. That being said, I saw a video on the internet of the most cocked up x-wind landing in a 146 ever. So you can get it wrong. Not me. But somebody.

[Trader]

The 777 recommended procedure is to land with at least partial crab in strong winds - good to 45 knots on a dry runway.

[Innuendo]

If you want to know how to side slip a large swept wing jet ask Bob Pearson, and he did not have any thrust at the time.

[Moon The Loon]

My preference on the 763 was to always land with the wings level. Using this technique, in a strong crosswind as J.O. pointed out above, especially on a "long-body", if the flight deck is over the centre line, one of the mains may be very close to the edge lighting on a 45M/150' wide runway requiring the flight deck be upwind of the CL markings/lights.

During those times, I found the technique worked, always. From time to time, using this cross-control-during-flare/touchdown technique, the nose would not always be perfectly lined up, but the mains touched down either side of the CL markings/lights, and the risk of dragging a pod (not as much a consideration on heavy twins) was reduced. I used to look ahead to flying the 74 or 340 with pods far outboard of the mains, and wanted a technique that worked universally.

Don't have to worry about that kind of flying anymore!!

[blues deville]

Do Airbus or Boeing publish a max crosswind limitation for any of their types or merely a max demonstrated crosswind?

I believe it is max demonstrated for Boeing who states this in their FCTM.

"Crosswind guidelines are not considered limitations. Crosswind guidelines are provided to assist operators in establishing their own crosswind policies."

My airline's x-wind limitation is below what Boeing has shown but are now trying to increase that number to the airplane's current max demonstrated.

[Mizar]

You "can", but you shouldn't. It's quite dangerous in a swept wing aircraft.

I question your analysis as it is wrong to make such a blanket statement. I have done plenty of sideslip approaches to crosswind landings in swept wing aircraft. Once the winds get beyond a certain strength, a sideslip alone may not be adequate depending on aircraft type and underslung engines can be another consideration as well. The type I fly now has in the manual that sideslip approaches are an approved technique.

And next time you do an autoland, look at how the approach is done. At least on my type, it is in a sideslip.

[conehead]

And next time you do an autoland, look at how the approach is done. At least on my type, it is in a sideslip.

Hmmmm.... Yeah, I think Jeff normally picks this phase of the flight to take a nap, he has no interest in what his aircraft is doing.

Really?

[HST]

I can't get a good read on your post conehead (sarcasm???) but in the absence of emotion thingy's I'll presume you are serious. One of the points I was trying to put across earlier (and repeated by Mizar) is that if sideslipping is so dangerous (as suggested above) why would Boeing (and other manufacturers) design an autoland system to do exactly that during one of the most critical phases of flight?

[Mitch Cronin]

if sideslipping is so dangerous (as suggested above) why would Boeing (and other manufacturers) design an autoland system to do exactly that during one of the most critical phases of flight?

... because computers can do some things much faster than human beings?

... also, wouldn't another consideration be fouling airflow into the downwind engines? How much sideslip would be too much? Are there charts for that in the AOM?

In any case, logic, to me, says that with swept wings in a slip at slow speeds, your downwind wing could get close to stall, or worse, pretty quickly.

[conehead]

I can't get a good read on your post conehead (sarcasm???) but in the absence of emotion thingy's I'll presume you are serious.

Sorry, it was sarcasm. Mizar was implying that J.O. was not aware of what the aircraft was "doing" during the Autoland approach. Seemed a bit condescending.

[Don Hudson]

Hi Mitch;

Re, ".. also, wouldn't another consideration be fouling airflow into the downwind engines? How much sideslip would be too much? Are there charts for that in the AOM?"

I don't think there are charts because I think the engines wouldn't care. It would take a huge angle before the engines would be upset. Example: - at impact with the sea, the engines on the A332 lost on AF447 were fully functioning at 98% and 100% for engines 1 & 2 respectively, with a forward speed of about 105kts, an angle-of-attack of around 41deg, a pitch angle of 16deg and a vertical speed of around 11,000fpm.

On the other question regarding the wisdom and risk of sideslipping a swept wing transport, DP Davies (HTBJ) agrees with J.O.'s assessment on large sideslip angles, (small ones being inevitable during initial engine failure, crosswind decrabbing, etc):

"It is wrong in principle to allow a swept wing aeroplane to suffer significant angles of sideslip. So, always use the rudder in the conventional sense to keep sideslip to small values.", (D.P. Davies, Handling the Big Jets, 3rd ed., CAA, p.265)

[Mitch Cronin]

True Don, but those were CF6-80's on the AF bird, which can take a pretty good cross-wind component. Some engines are quite a bit more sensitive... at least for ground runs, which I know is not what we're talking about.... but we DO have allowable crosswind charts for that. For some engines, anything more than 10kts at 90 degrees will be verboten. If 447 had Pratts, they might have been barking on the way down (with less than 30kts fwd airspeed!).

[Mitch Cronin]

I always thought Dutch roll was just bloody uncomfortable, and fighting it was very tiring, so that's what led to the yaw damper? .... I wouldn't think it would be much of a challenge when one is intentionally crossing controls to slip?

[boestar]

My thoughts exactly Mitch. Dutch roll can be induced on a swept wing aircraft in level flight in calm air and thats what the Yaw Damper is controlling. If the aircraft is intentionally slipped, the Yaw Damper couldn't care less as the aircraft is doing what it is told. It will continue to dampen the roll ocillations though even in the slip.

[DEFCON]

Dutch roll can lead to a complete loss of control. In addition to yaw dampers, real slippery aircraft employ fuselage strakes to keep the aircraft tracking straight

[HST]

because computers can do some things much faster than human beings?

Mitch, having witnessed this more than a few times, autopilot computer coordination of control surfaces (which feeds in these cross control inputs slowly) below 400' RA (versus the speed at which this is done) is likely the answer here.

This thread is 'slipping' in the wrong direction. I contend that using one of the manufacturer's 3 recommended crosswind landing techniques (using sideslip to remove approx. 80% of drift) in the final stages of the approach (emulate the autopilot, if you will) and well within the manufacturer's limits, isn't dangerous.

[Don Hudson]

From Fundamentals of Flight:

Dynamic Lateral Stability

. . . .

"The second lateral motion is an oscillatory combined roll and yaw motion called Dutch roll because of its similarity to an ice-skating figure of the same name. The Dutch roll may be described as a yaw and roll to the right, followed by a recovery and roll to the left, then back past the equilibrium attitude, and so on. The period is usually of the order of 3 to 15s. Damping is increased by large directional stability and small dihedral and decreased by small directional stability and large dihedral. Although usually stable in a normal airplane, the motion may be so slightly damped that the effect is very unpleasant and undesirable.

"Swept wing aircraft have large dihedral stability even when they have no dihedral angle. This arises because the effect of an angle of yaw is to increase the sweepback angle of one wing panel and decrease it for the other side of the airplane. The change in sweep alters the effective dynamic pressure normal to the quarter-chord line of the wing panel, increasing the lift on one side of the wing, lowering it on the otherside, and producing a restoring rolling moment. Nevertheless, many swept wing airplanes have a considerable dihedral angle, not for aerodynamic reasons but to give adequate ground clearance for the wing tips and wing-mounted nacelles during landing and takeoff. These aircraft may then have too much dihedral effect for satisfactory Dutch roll damping. The problem is solved by instilling a yaw damper, in effect a special-purpose automatic pilot that damps out any yawing oscillation by applying rudder corrections. Some swept wing aircraft have an unstable Dutch roll mode. If the Dutch roll is very lightly damped or unstable, the yaw damper becomes a safety requirement rather than a pilot and passenger convenience. Dual yaw dampers are required and a failed yaw damper is cause for limiting flight to lower altitudes, and possibly lower Mach numbers, where the Dutch roll stability is improved." - Fundamentals of Flight, Richard S. Shevell, p.307

HST;

If it's in the book, by all means use it as intended by the manufacturer. The thread's drifted a bit but I think in a worthwhile way. Thanks for the reminder.

[Moon The Loon]

Bear in mind that Boeing (BFCTM) and I suspect Airbus will put in your SOP document anything you like, so long as it is not a violation of the aircraft certification or secondly, it is not unsafe. Boeing stated in its Icelandic 757/767 SOP that it is OK to takeoff with frost over the cold-soaked fuel tanks so long as one could read the writing (aircraft ID) through the frost. On the upper surface of the wing, no less. Didn't work for me, but that's what they allowed. So much for manufacturer's recommendations. Automation is not a God. Don't let It or the "manufacturer's recommendations" overrule common sense.

The autoland may very well sideslip. I've seen it on the Boeing autolands. They don't like crosswinds! Even with multiple autopilots. Very, VERY uncomfortable procedure.

When hand-flying the landing, ask one's self: what works best every time, all the time? You're on the ILS or RNAV/VNAV path from 10 miles out. Wind constant all the way to DA(H)/MDA - the wings are level; the heading offset for the wind. Changing those inputs at 200' or 100' for a manual landing is a means of destabilizing your approach, is it not?

Then add to the problem the outboard pods on aircraft such as the A340-600.

Why would one ever consider side-slipping?

Hence my past practice of what works best every time, always.

Just questions. Just questions....