Wisdom of side-slipping a large jet?

[Oilhead]

I was just asked by another pilot whether is it is legal to side-slip a large jet or not. I am uncertain of the "legality" answer and thought it might be a good discussion item. In one crosswind landing technique, one slips a plane when we kick off crab in the flare; on another technique, it is taught to straighten the plane further back up the approach and effectively slip it down to the landing from say 200 or 300 feet. That is a low speed landing manoeuvre which is not likely to damage the aircraft. However the person who posed this question is referring to using side-slip much further back up the approach, in much the same manner as a Piper Cub etc. that is too high and too fast! My thoughts are that it is a most inappropriate and unwise way to fly a large plane such as a 757, and I am curious as to other pilots thoughts. I would be very concerned about structural integrity of the vertical fin as well as other safety/comfort issues.

While I am sure many would join me in being basically appalled at the idea of flying a transport category aeroplane like that, I am curious as to what certification/flight testing has been done on a new model. If it has not, then why is it not listed as a specifically banned maneuvre?

OH

[Rick Studder]

I see nothing wrong in using more or less subtle sideslipping as a crosswind technique long before the de-crab in the flare, it is described as one of the standard techniques in my SOP also (B767). But sideslipping a large jet to lose altitude if high on approach does not sound like a good idea, rather the need for it would indicate an unstable approach and a go-around.

[SNS3Guppy]

You're questioning the wisdom of sideslipping a swept wing airplane at low speeds and low altitude...and wonder about the effects?

What is the effect of altering the airflow such that it's more perpendicular or normal to the leading edge on one wing, and less on the other? Think about it.

Yes, the structural integrity of the vertical stab should be closely considered. I flew large airplanes in an operation that involved regular slipping throughout the flight, and discovered cracking in attach brackets and bolts, and after careful consideration, quit slipping airplanes under those or nearly any other circumstance.

[hetfield]

Side-slipping 300 or more pax?

Common, switch to aerobatics.

[XPMorten]

Makes me think of thisone...

http://www.break.com/index/insane-landing-in-honduras.html

M

[FlyMD]

I was sitting in the right seat of an MD83 about 15 years ago, when the old guy misjudged a visual approach and put it in a full-rudder-deflection sideslip to lose altitude on finals...

Whilst he did it smoothly enough so i didn't worry about structure, and had enough speed on not to worry too much about stall margins, I SWEAR i saw the EGT of the "downwind" engine rise about 100 degrees, enough to start me sweating... something else to think about when u sideslip an airplane with this kind of engine configuration...

[World of Tweed]

When an Air Canada 767 ran out of fuel near winnepeg in the early eighties it became the worlds largest glider...... everyone survived though.

How do you think they lost the height to bring her down to a disused air force base? They side-slipped her several times, the guy was a keen glider pilot apparently.

Whilst it is not a normal technique they are still aeroplanes and if needs must..... then slip away..... I'd much prefer to just do an orbit though.

[Loose rivets]

I've often thought about this problem. Over a short period of my career, I was able to fly an assortment of aircraft much as I pleased. There were no passengers...paying ones that is.

My main concern was for the airflow into the engines, (Darts and Speys) but despite quite dramatic maneuvers, there seemed little change in the displayed temps. Huge amounts of energy could be dissipated by slipping, and when returning to normal line flying it was certainly a comfort to know that I could achieve a very steep glide should it become necessary in an emergency.

As for the load on the (T) tail. Well the aircraft was brick-built, so it's hard to compare to modern kit, but gentle entry into the maneuver was just a natural precaution, it was coming out of the slip that was difficult to do gently.

DC3s were an interesting aircraft to slip. Full rudder was an almost everyday event in bush-style flying. It was one @#$% difficult airplane to get out of the sky. Dirty as you could make it, and full rudder, and it still took something like (from distant memory) 5 mins to loose 9kfeet. An awful long time if you're on fire.

[Dani]

According to my experience, most of manufactor and operator recommend only partial decrabbing during landing. Apart from that, noone ever speaks of side-slipping.
There are people who decrab before flare and others during flare. On wet/contaminated you tend to decrab less than on dry. But basically you can decrab every aircraft during a crosswind landing. Apart from that, you don't.

Dani

[misd-agin]

Part of the AA 587 investigation focused on rudder use. Recall is that the manufacturers state that rudder is for s/e and crosswind controls.

Post 9/11 pilots talked about using yawing actions as defensive manuevers. Manufacturers printed guidance against that technique.

Can they sideslip? Yes. Will they fall apart? Uh, no. However keep in mind cross controling is also a spin/departure entry technique.

The question becomes if you really need to slip the a/c are there better alternatives(G/A, missed approach, etc) that would be more prudent to use?

[matt_hooks]

For modern flying, into fully equipped airports with ILS approaches, you should never be in a position where you need to lose a lot of height very quickly.

As long as you have the GS and LOC within limits, and have a recommended approach speeds, sideslipping is unnecessary.

If you are in a position where you require a sideslip in order to lose energy, then something has already gone wrong and I would suggest a go-around and repositioning to land would be the safe option rather than flying untested manouvers.

If there's any doubt, there's no doubt!

[Dan Winterland]

Yes, in an ideal world. But when I flew 747s into the USA, one of our destinations used to keep us very high on approach to deconflict traffic with another nearby airport in certain wind directions. The guy who did my line training showed me how he coped. It was gear down, full flap and a very small and barely perceptable sideslip! It worked and I used it subsequently. However, be aware that on swept wing aircraft, The secondary roll effect of rudder is very very powerful, so you use a tiny amount of rudder and quite a lot of aileron.

[Loose rivets]

For modern flying, into fully equipped airports with ILS approaches, you should never be in a position where you need to lose a lot of height very quickly.


This is what worries me about modern thinking. You might go the whole of your career without a single serious malfunction, or you might be thrown in at the deep end way before you get your command. Things can get seriously out of kilter sometimes.

I was in the RHS of a shiny new jet when in my mid twenties and the guy in the left just lost it...I mean really came unglued. We were in a storm and surrounded by mountains. On that day (and one other in my career ) I took control of the airplane and used some rather ‘basic' techniques to get on the ground. There was one granite free way to go on a go-around, and that was into the core of the storm. Right or wrong, to my young brain, the rain lashed airfield looked a lot more inviting.

Everything that happened was helped by the fact that we did our training on the real hardware, the training staff were steep on the learning curve and we saw things done by the manufacturers pilots that you would never see today.

Trying to balance on a knife-edge of careful SOPs flying while everything is going wrong, just doesn't hack it.

[Rick Studder]

Out of curiousity: How would you sideslip an airbus? I suppose you would command a certain roll rate uisng the side-stick, which would then return to neutral, while holding continual rudder input in opposite direction. I take it the rudder on the bus functions in 'direct law', i.e. as in conventinal aircrafts? Have a feeling the sideslip manoeuvre would seem a bit peculiar in the bus.

[cwatters]

Err Am I mistaken or are some people confusing crabbing and sideslipping? Sideslipping involves slip whereas crabbing doesn't (at least not normally)...
Crabbing involves adjusting the heading to correct for crosswind (eg so the ground track equals runway heading). The yaw string should remain in the centre as will the controls once the heading is correct. It's relativly safe as the plane is "flying normally".
Side slipping involves making the plane fly sideways by the application of yaw. It usually requires some control input to maintain the slip or the plane "flys out of it". Some planes require "opposite" aileron to hold the leading wing down and prevent the plane rolling in response to the rudder input. The stalling speed is increased so there is some risk. Keep the speed up but not too high or the rudder/fin will fall off.
..at least that's how I understand it.

edit: Oh well I guess I was hasty posting this. Just read this thread again and it seems nobody is confused. I'll go back to my beer.

[matt_hooks]

Rivets, of course I agree. There ARE occasions when you need to do extraordinary things, but in the most part it is not a necessary manouver.

So yes it's good to have these things up your sleeve, but most pilots will never use them.

[411A]

A rather bad idea to aggressively side/forward slip a large jet aeroplane, with pod mounted engines on the wings.

Besides initiating rather high rates of descent there have been cases in the past where aggressive forward slips have resulted in engine pylon damage...as in, slightly bent.

Engine pylons are not designed for this type of maneuver, just as aggressive use of a powered rudder at higher speeds has resulted in....bad news.

If I, as a TRE/IRE, noticed an aggressive slip being used, the line check would be...failed, and the concerned pilot sent packing.
These types of maneuvers have NO business being used on a large heavy jet transport.
Period.

[Loose rivets]

As an examining captain, you would have no choice but to fail someone that slipped a large aircraft...but that's not the point. It's the absolute absence of the skill "up one's sleeve" that worries me.

Based on nothing more than a gut feeling, I would doubt that side-load airflow alone would damage a pylon, bearing in mind that slipping, if done at all, would be at low speed. However, I would readily accept that the lateral accelerations and complex rotational g-forces would have to be kept to an absolute minimum. Johnson's maneuvers come to mind.

I recall a very respected training captain in the early 60s, who would take us over the threshold at 1,500 feet, and tell us to land. It was a simple and fun exercise, and the fact that I can remember it so clearly all these years later, must mean that it was well ingrained.

Another captain used to push us into doing a 60 degree bank turns at 500 at Teeside. I still recall him chuckling as I put on full noise. Great fun and such a good grounding in learning the feel.

[Trolle]

Read an article way back that Alaska Airlines were certified to use side slips into specific destinations. At the airlines I have been never been certified nor mentioned in the manuals. Tried it in the sim though. Airflow changes and other events may have an interesting affect. Should always be able to perform one though as you never know when you might need it.
Nomenclature:
Side slip - longitudinal axis is parallel with centerline in cross-controlled situation (x wind landing)
Forward slip - longitudinal axis is not parallel with centerline in cross-controlled situation; more rudder than aileron (increase rate of descent without increasing airspeed)

[FullWings]

In all the aeroplanes I've flown, including big jets, it was possible to perform a controlled sideslip with no worries about the fin coming off/one wing stalling/engine(s) blowing up. That still leaves a lot of aeroplanes, I admit, but taking into account basic aerodynamics, the reality of pilot inputs and motions of the atmosphere, any 'plane must be able to withstand some element of sideslip otherwise it would come apart in normal operation. Not to mention asymmetric flight.

I'm not saying it's a good idea to top-rudder your 747 round finals into a sideslip whilst on a line check. (Tempting, though... :E) It might become a useful tool in more extreme cirumstances, i.e. high and must land, everything hanging out, still overshooting. A danger is the sheer power of most aircraft rudders and thus the need to be reasonably smooth and controlled when playing with your feet. (Which airline pilots are told to use a little as possible - for good reason.)

When an aircraft gets airborne in a crosswind, it is in a (temporary) slipping condition. When you land 'wing down' the same applies. When flying asymmetrically, the yawing moment of the engine(s) is opposed by rudder & fin loads, with some lateral control deflection if necessary (or the other way round if you want to!). These situations are tested as part of certification: at Vmca, full control deflection is probably required.

[GROUNDSTAR]

The fins of large aircraft are not designed to withstand the stresses induced from side loads (at and below Va = design manoeuvring speed) other than during normal flight ops, turbulence and single engine operation. The A300 accident in New York was simply due to mishandling rather than aircraft design flaw. Structural failure is likely to occur in any medium/large jet if handled in the same manner. To quote the flight manual 'Sudden commanded full, or nearly full, opposite rudder movement against a sideslip can generate loads that exceed the limit loads and can result in stuctural failure....CERTIFICATION REGULATIONS DO NOT CONSIDER THE LOADS IMPOSED ON THE STRUCTURE WHEN THERE IS SUDDEN FULL, OR NEARLY FULL, RUDDER MOVEMENT THAT IS OPPOSITE THE SIDESLIP'. (FCOM Bulletin No.827/1)
That said, I'm not sure if the original post was confusing wing down vs crab technique, with sideslip technique.

[ERJFO]

This isn't dangerous just because of airframe stress. Think about the aerodynamic implications of side-slipping a SWEPTWING aircraft. The downwind wing's "sweep angle" is rapidly increased causing airflow over the wing to slow thus decreasing lift substantially. The oposite is happening on the upwind wing. (Think of it as a sort of Dutch-Roll.) Not only can the downwind wing ubruptly stall but the upwind wing can quickly rise due to the increase in life on that side. This is how a spin happens. All of this is exagerated by flap deployment.

The above senario could be terrible not to mention the effects of the sideslip on the engines (possible airflow reductions, over-temps, compressor stalls).

Bottom-line, sidesliping a large, swept-wing, turbine powered airplane close to the ground could go bad very fast.

[Gullyone]

I did it once on a BCAL DC10. I was on a line check and I was a bit to fast to lower the gear. As I was about to intercept the glide I gave it a tad of rudder, lost a few knots and set of down the glide. I expect the trainer noticed but nothing said and I passed the check.
Happy days

[GROUNDSTAR]

ERJFO,
That's quite right, also relative airflow over the upwind wing will act at a more normal angle to the angle of sweep (also reduced spanwise flow) thereby producing more lift hence the tendancy for that wing to try to pick it self up (inherant stability of swept wing) thus in theory it's quite difficult to sideslip a swept wing aircraft in the first place.

[Loose rivets]

I'm not sure that your analysis of what's going on is correct. I don't know, but I'm not sure...if you know what I mean.

When the aircraft is in a stable side-slip, one would assume that it is descending. The wing loading will be reduced and the stall put back to comfortable distance from the airspeed over any part of either wing. Furthermore, a proportion of the aircraft's weight will be cushioned on the lower fuselage side, further reducing the chance of a stalled wing.

My reservations however, are in two parts. One, it would be difficult to assess the load on the tail without very skilled calculations. Two, the engine temps may not be showing some hidden parameters that they were never intended to display. But, I have seen huge loads on our brick built BAC1-11's tail, due to the strangest of occurrences. And I have seen the engine parameters showing extraordinary fluctuations due to other circumstances. During prolonged and repeated side-slips, I never saw the slightest variation in temps, just a little change in EPR

[ratarsedagain]

When an Air Canada 767 ran out of fuel near winnepeg in the early eighties it became the worlds largest glider...... everyone survived though.

How do you think they lost the height to bring her down to a disused air force base? They side-slipped her several times

Don't suppose they were particularly worried about airflow and stall margins through the engine though;)

[747dieseldude]

Ain't so large, but still a swept wing jet,
the CL-600 Challenger has a procedure for balancing fuel in cruise using side-slip.

Ain't that something?

[BadBigbusBoy]

good site for info : http://www.airbus.com/store/mm_repository/safety_library_items/att00007639/media_object_file_FLT_OPS-LAND-SEQ05.pdf

[John Farley]

That has to be the best write up I have seen on the topic of crosswing landings.

[777fly]

I agree with 'TROLLE' in his previous posting. There is a distinction between a steady state sideslip (as in a cross wind) and a forward slip, which is the technique used on light aircraft to lose excess height during approach.
I believe that the original posting on this thread was assess the relative safety of getting a swept wing transport into a forward slip in order to get height off.
The B777 flying manual specifically recommends setting up a steady state side slip in crosswind conditions and a max bank angle of 5 degrees is quoted. In limiting conditions ( 30-35kts crosswind) around 10 degrees of drift needs to be ruddered off and a control wheel deflection of 30-40 degrees results in order to keep the bank angle to approx 5 degrees. Therefore a sideslip manoeuvre IS permitted on swept wing aircraft, under specific conditions.
However,as in any sideslip, there is increased drag from greater control surface deflection and spoiler deployment on the raised wing, plus a loss of vertical lift component due to the bank angle. All of this results in an increased rate of descent on the B777 (or any jet) which has to be counteracted by a small increase in pitch attitude. If not, the aircraft will go low on the approach path. Within these parameters a small degree of sideslip MIGHT be used in non-crosswind conditions to lose height at constant speed.
If a similar technique were to be used in a forward slip in order to deliberately lose a substantial amount of height, it would be very easy to reach a point where where the rudder input would require full (limited) control wheel deflection in roll, to oppose the rudder . I would guess that this would occur at an offset heading of around 15-20 degrees, which is not a lot, visually. Would you really want to be at a control limit position at a high rate of descent close to the ground? Given the powerful roll/yaw couple of a jet transport, your sudden relaxation of the roll input when it is realised that roll control is being limited or lost could rapidly lead to to an uncontrollable roll-off at low altitude.

[777fly]

RE :previous posting, please read as 'spoiler deployment on lower wing' NOT the raised one!

[p7lot]

This has to be one of the best......

http://www.liveleak.com/view?i=cb4_1172351204&p=1