Sideslip or De-crab in the flare

[typhoonpilot]

MDC has tended towards side-slips in more recent types.

Ummm, but their most recent type was the 717 certified in 1999. When I flew the DC-9/MD-80/MD-90, and instructed in Long Beach for McDonnell Douglas, I was firmly in the sideslip camp. We grow as professionals though. There is a whole world of airlines outside of the USA and manufacturers in the corporate world that advocate de-crab in the flare. I have not flown the DC-10/MD-10/MD-11 so can't comments specifically what will work best for you, but try the de-crab next time you are in the sim. Allocate more than a few tries though, it takes some practice to get the timing right.


Typhoonpilot

 

[seagull]

Ummm, but their most recent type was the 717 certified in 1999. When I flew the DC-9/MD-80/MD-90, and instructed in Long Beach for McDonnell Douglas, I was firmly in the sideslip camp. We grow as professionals though. There is a whole world of airlines outside of the USA and manufacturers in the corporate world that advocate de-crab in the flare. I have not flown the DC-10/MD-10/MD-11 so can't comments specifically what will work best for you, but try the de-crab next time you are in the sim. Allocate more than a few tries though, it takes some practice to get the timing right.


Typhoonpilot

The 717 is really a DC-9 in terms of handling qualities and as I recall they piggy-backed much of the cert based on that fact. The DC-10 and MD-11 advocate the side-slip, as apparently, does the C-17, the latter truly being the most recent in all respects.

 

[SlumTodd_Millionaire]

The 717 is really a DC-9 in terms of handling qualities

Hell, it's a DC-9 in virtually every respect except the cockpit.

 

[typhoonpilot]

The 717 is really a DC-9 in terms of handling qualities and as I recall they piggy-backed much of the cert based on that fact. The DC-10 and MD-11 advocate the side-slip, as apparently, does the C-17, the latter truly being the most recent in all respects.

Leads me to wonder what crosswind landing technique was used during all of these accidents?:

1994, November 4. A Fed Ex MD-11 freighter made a hard landing, and a tail strike at the Anchorage, Alaska airport. After selecting 50 degrees of flaps the first officer, who was flying the plane, was not able to stabilize the approach in the pitch mode. The attitude of the plane varied approximately 2 degrees with corresponding elevator position changes. The captain, because of the high sink rate, grabbed the yoke and pulled back. The plane landed hard, bounced, and oscillated at least three times, reaching a maximum pitch up attitude of 12.3 degrees. The tail struck the runway during the oscillations. This was also the plane that crashed at Newark in 1997.

1997, July 31. A Fed Ex MD-11 bounced on landing at Newark airport and then flipped upside down off runway 22 R. The two pilots and three passengers managed to escape before the plane was destroyed by fire. The investigation is focusing on the failure of the right main gear, which allowed the right engine and wing to dig into the ground, flipping the plane over.

1999, August 22. A China Airlines MD-11 crashed while landing at Hong Kong’s Chek Lap Kok airport, during a rain storm with strong, gusting crosswinds. The right gear struck the runway very hard and then broke off, allowing the right engine and wing to strike the ground. The right wing then broke off and the plane flipped upside down. That is very similar to the type of damage incurred by the Fed Ex MD-11, when it crashed at Newark. Three of the 315 people on board Flight C1642 were killed. The rest owe their lives to the Hong Kong airport’s fire brigade that put out the fire before it engulfed those trapped in the wreckage. It took almost 3 hours to remove all the survivors.

2001, November 20. An Eva Air MD-11 made a hard landing at Taipei, Taiwan. The first officer was flying the plane as it hit hard and bounced. The captain immediately took control and initiated a successful go-around. After the second landing, investigation revealed substantial damage to the nose wheel well structure and one of the two nose tires had failed.

23 March 2009; FedEx Express MD-11F; Flight 80; near Tokyo, Japan: The aircraft was on a cargo flight from Guangzhou, China to Narita Airport near Tokyo, Japan. The aircraft bounced on landing, and contacted the runway a second time nose wheel first before rolling to the left, contacting the runway with its left stabilizer and wing, and catching fire. The aircraft ended up in an inverted position. Both crew members were killed.

27 July 2010; Lufthansa; MD-11F; flight 8460; Riyadh, Saudi Arabia: The aircraft was on a cargo flight from Frankfurt, Germany to Riyadh, Saudi Arabia had a landing accident that fractured the fuselage. The two crew members survived.



Typhoonpilot

 

[Groundpounder]

How about this technique?

 

[typhoonpilot]

Landing in a crab on a slippery runway is okay per Boeing. Not what I would do, but it is discussed in the Flight Crew Training Manual.


TP

 

[seagull]

Leads me to wonder what crosswind landing technique was used during all of these accidents?:

1994, November 4. A Fed Ex MD-11 freighter made a hard landing, and a tail strike at the Anchorage, Alaska airport. After selecting 50 degrees of flaps the first officer, who was flying the plane, was not able to stabilize the approach in the pitch mode. The attitude of the plane varied approximately 2 degrees with corresponding elevator position changes. The captain, because of the high sink rate, grabbed the yoke and pulled back. The plane landed hard, bounced, and oscillated at least three times, reaching a maximum pitch up attitude of 12.3 degrees. The tail struck the runway during the oscillations. This was also the plane that crashed at Newark in 1997.

1997, July 31. A Fed Ex MD-11 bounced on landing at Newark airport and then flipped upside down off runway 22 R. The two pilots and three passengers managed to escape before the plane was destroyed by fire. The investigation is focusing on the failure of the right main gear, which allowed the right engine and wing to dig into the ground, flipping the plane over.

1999, August 22. A China Airlines MD-11 crashed while landing at Hong Kong’s Chek Lap Kok airport, during a rain storm with strong, gusting crosswinds. The right gear struck the runway very hard and then broke off, allowing the right engine and wing to strike the ground. The right wing then broke off and the plane flipped upside down. That is very similar to the type of damage incurred by the Fed Ex MD-11, when it crashed at Newark. Three of the 315 people on board Flight C1642 were killed. The rest owe their lives to the Hong Kong airport’s fire brigade that put out the fire before it engulfed those trapped in the wreckage. It took almost 3 hours to remove all the survivors.

2001, November 20. An Eva Air MD-11 made a hard landing at Taipei, Taiwan. The first officer was flying the plane as it hit hard and bounced. The captain immediately took control and initiated a successful go-around. After the second landing, investigation revealed substantial damage to the nose wheel well structure and one of the two nose tires had failed.

23 March 2009; FedEx Express MD-11F; Flight 80; near Tokyo, Japan: The aircraft was on a cargo flight from Guangzhou, China to Narita Airport near Tokyo, Japan. The aircraft bounced on landing, and contacted the runway a second time nose wheel first before rolling to the left, contacting the runway with its left stabilizer and wing, and catching fire. The aircraft ended up in an inverted position. Both crew members were killed.

27 July 2010; Lufthansa; MD-11F; flight 8460; Riyadh, Saudi Arabia: The aircraft was on a cargo flight from Frankfurt, Germany to Riyadh, Saudi Arabia had a landing accident that fractured the fuselage. The two crew members survived.



Typhoonpilot

Not all of them had crosswinds. I have, personally, worked on a few of those, and analyzed performance for all of them in the course of that work. Nothing to do with crosswind technique, although I could see an argument that using a kick-out method could exacerbate coupling problems in any of them, if they had used it.

 

[typhoonpilot]

Not all of them had crosswinds. I have, personally, worked on a few of those, and analyzed performance for all of them in the course of that work. Nothing to do with crosswind technique, although I could see an argument that using a kick-out method could exacerbate coupling problems in any of them, if they had used it.

Using the term "kick-out" shows a lack of experience with using a proper de-crab in the flare technique. As I stated earlier, try the de-crab in the flare technique in the simulator a few times until proficient with it. Start with smaller crosswinds and then gradually increase them to the maximum demonstrated for the aircraft type. It does take a while to get the technique down smoothly. At that proficiency level there would be no "exacerbation of coupling problems". On the other hand, a sideslip technique will result in an increase in descent rate. Perhaps enough to drive the main wheels through the wing or break the spar.



Typhoonpilot

 

[Deleted member 27505]

There is a good discussion going on in a thread on PPW:

http://forums.propilotworld.com/showthread.php?98159-Technique-for-X-wind-and-HUD

Just thought I would expand the discussion to here and include a poll.


Typhoonpilot

It's been my experience that it depends upon the equipment you're flying. Jets with lots of sweep and low slung engines don't slip very well. So I want answer D: both.

 

[seagull]

Using the term "kick-out" shows a lack of experience with using a proper de-crab in the flare technique. As I stated earlier, try the de-crab in the flare technique in the simulator a few times until proficient with it. Start with smaller crosswinds and then gradually increase them to the maximum demonstrated for the aircraft type. It does take a while to get the technique down smoothly. At that proficiency level there would be no "exacerbation of coupling problems". On the other hand, a sideslip technique will result in an increase in descent rate. Perhaps enough to drive the main wheels through the wing or break the spar.



Typhoonpilot

Typhoon,

All due respect, I used the technique for many years in DC-8-73s, 727s and other aircraft. To argue that the term shows "lack of experience" is a bit inane, frankly. I think 20+ years of doing it in large transports, regardless of what term you wanted to use for it, should qualify someone as "experienced". I found the technique better than a side-slip (now called a "wing low method" in a similar vein as "proper de-crab"), but have used both with success. I have also done it on the -10 and -11 in the past, and it worked fine there too. I always found it more comfortable and allowed for greater crosswind capability. I did it in light tricycle gear airplanes also, for that matter, and taught it for many years. The OEM on the -11 advises that the side-slip be used. I am not sure how they came to that, but I will find out. I can tell you for absolute certainty that it has NOTHING to do with any of the accidents. I might add that your response appears to indicate that you might not understand the "coupling" issues that I am talking about. No amount of proficiency will reduce a coupling issue. Also, a side-slip should not result in any increase in ROD if done correctly. Yes, it initially adds drag, but if it is compensated with power it is a non-issue.

 

[Deleted member 27505]

Ummm, but their most recent type was the 717 certified in 1999. When I flew the DC-9/MD-80/MD-90, and instructed in Long Beach for McDonnell Douglas, I was firmly in the sideslip camp. We grow as professionals though. There is a whole world of airlines outside of the USA and manufacturers in the corporate world that advocate de-crab in the flare. I have not flown the DC-10/MD-10/MD-11 so can't comments specifically what will work best for you, but try the de-crab next time you are in the sim. Allocate more than a few tries though, it takes some practice to get the timing right.


Typhoonpilot

Actually, it just takes learning to fly in a taildragger and discovering the immutable reality that yaw, and bank, and pitch are all connected and hitched and when you change one, you gotta change the others. Oh! the horror!

 

[typhoonpilot]

Typhoon,

All due respect, I used the technique for many years in DC-8-73s, 727s and other aircraft. To argue that the term shows "lack of experience" is a bit inane, frankly. I think 20+ years of doing it in large transports, regardless of what term you wanted to use for it, should qualify someone as "experienced". I found the technique better than a side-slip (now called a "wing low method" in a similar vein as "proper de-crab"), but have used both with success. I have also done it on the -10 and -11 in the past, and it worked fine there too. I always found it more comfortable and allowed for greater crosswind capability. I did it in light tricycle gear airplanes also, for that matter, and taught it for many years. The OEM on the -11 advises that the side-slip be used. I am not sure how they came to that, but I will find out. I can tell you for absolute certainty that it has NOTHING to do with any of the accidents. I might add that your response appears to indicate that you might not understand the "coupling" issues that I am talking about. No amount of proficiency will reduce a coupling issue. Also, a side-slip should not result in any increase in ROD if done correctly. Yes, it initially adds drag, but if it is compensated with power it is a non-issue.

Yes Shem, I understand that you like to use academic terms for simple concepts. Pilot Induced Oscillation is what you are referring to when you say coupling. The actual definition of coupling is here:

noun

1. a mechanical device that connects two things
2. a device for connecting railway cars or trucks together
3. the part of the body of a horse, dog, or other quadruped that lies between the forequarters and the hindquarters
4. (electronics) the act or process of linking two or more circuits so that power can be transferred between them usually by mutual induction, as in a transformer, or by means of a capacitor or inductor common to both circuits See also direct coupling
5. (physics) an interaction between different properties of a system, such as a group of atoms or nuclei, or between two or more systems
6. (genetics) the occurrence of two specified nonallelic genes from the same parent on the same chromosome
7. Can also be used for sexual mating.

Here is your definition:

The NRC states: “Aircraft-pilot-coupling (APC) events” are inadvertent, unwanted aircraft attitude and flight path motions that originate in an anomalous interaction between the aircraft and the pilot.

Now that everybody knows that you actually meant PIO, let's discuss that. A properly flown de-crab in the flare involves flying the approach in a crab all the way into the flare. Once the flare has started, and just prior to touchdown, downwind rudder is applied to eliminate the crab and align the airplane with the runway centerline. As rudder is applied, the upwind wing sweeps forward developing roll. In order to hold the wings level simultaneous application of aileron control into the wind is applied. Done properly and with the correct timing I fail to see how a PIO can develop since this is done just prior to touchdown.

You must agree that FedEx and the MD-11 have had some serious issues with landing accidents. The pilots who write the procedures at the manufacturer are no smarter than you or me. I think you'll find that MDC was biased towards the sideslip technique from their history and just never kept up with industry trends. I do not believe there can be any argument that a sideslip does not, at least momentarily, increase descent rate. We all learned that from early flight training. To do so at low altitude in a swept jet is just not the safest way to fly for so many reasons: increased descent rate; wing low increasing risk of striking a surface on the pavement; etc; etc. As a safety advocate I fail to see why you are being so obstinate. Just look at the poll results above.



Typhoonpilot

 

[seagull]

Yes Shem, I understand that you like to use academic terms for simple concepts. Pilot Induced Oscillation is what you are referring to when you say coupling. The actual definition of coupling is here:

noun

1. a mechanical device that connects two things
2. a device for connecting railway cars or trucks together
3. the part of the body of a horse, dog, or other quadruped that lies between the forequarters and the hindquarters
4. (electronics) the act or process of linking two or more circuits so that power can be transferred between them usually by mutual induction, as in a transformer, or by means of a capacitor or inductor common to both circuits See also direct coupling
5. (physics) an interaction between different properties of a system, such as a group of atoms or nuclei, or between two or more systems
6. (genetics) the occurrence of two specified nonallelic genes from the same parent on the same chromosome
7. Can also be used for sexual mating.

Here is your definition:

The NRC states: “Aircraft-pilot-coupling (APC) events” are inadvertent, unwanted aircraft attitude and flight path motions that originate in an anomalous interaction between the aircraft and the pilot.

Now that everybody knows that you actually meant PIO, let's discuss that. A properly flown de-crab in the flare involves flying the approach in a crab all the way into the flare. Once the flare has started, and just prior to touchdown, downwind rudder is applied to eliminate the crab and align the airplane with the runway centerline. As rudder is applied, the upwind wing sweeps forward developing roll. In order to hold the wings level simultaneous application of aileron control into the wind is applied. Done properly and with the correct timing I fail to see how a PIO can develop since this is done just prior to touchdown.

You must agree that FedEx and the MD-11 have had some serious issues with landing accidents. The pilots who write the procedures at the manufacturer are no smarter than you or me. I think you'll find that MDC was biased towards the sideslip technique from their history and just never kept up with industry trends. I do not believe there can be any argument that a sideslip does not, at least momentarily, increase descent rate. We all learned that from early flight training. To do so at low altitude in a swept jet is just not the safest way to fly for so many reasons: increased descent rate; wing low increasing risk of striking a surface on the pavement; etc; etc. As a safety advocate I fail to see why you are being so obstinate. Just look at the poll results above.



Typhoonpilot

I fully understand how to fly the de-crab technique, and have used it on literally many hundreds of crosswind landings.

OK, first, PIO is more properly called APC, but nevermind that. I am not talking about PIO/APC at all. While that is a form of coupling, the term in this case discusses how one thing impacts another, take the physics definition (5) from your list. In this case the coupling is referring to the changing airspeed which is coupled with change in pitch coefficients, which are further related to the height and the impact of GE on pitch, aerodynamic center, center of lift, coefficient of lift for the wing and the stabilizer (THS). It alters the downwash gradient depsilon/dalpha, increases the tail effectiveness and also increases the "stiffness" term in the short period equation, which in turn reduces the SPO damping. It also increases the tail contribution to SPO damping.

Adding in the drag increase of the decrab right at that critical point is exactly WHY it increases the other coupling, relatively. No amount of "finesse" will change that.

 

[seagull]

As for the sideslip, MDC recommends it be entered by 200-300 feet, which allows plenty of time to compensate for the associated increase in drag, even if one just lets the A/T do it. I never have liked the technique, and you may be right as to why they went that way, but I have an email out to find out for sure.

 

[SlumTodd_Millionaire]

Nerd fight!

My money is on @seagull.

 

[typhoonpilot]

I fully understand how to fly the de-crab technique, and have used it on literally many hundreds of crosswind landings.

OK, first, PIO is more properly called APC, but nevermind that. I am not talking about PIO/APC at all. While that is a form of coupling, the term in this case discusses how one thing impacts another, take the physics definition (5) from your list. In this case the coupling is referring to the changing airspeed which is coupled with change in pitch coefficients, which are further related to the height and the impact of GE on pitch, aerodynamic center, center of lift, coefficient of lift for the wing and the stabilizer (THS). It alters the downwash gradient depsilon/dalpha, increases the tail effectiveness and also increases the "stiffness" term in the short period equation, which in turn reduces the SPO damping. It also increases the tail contribution to SPO damping.

Adding in the drag increase of the decrab right at that critical point is exactly WHY it increases the other coupling, relatively. No amount of "finesse" will change that.

Shem:

None of that matters when you are only 10 feet above the ground. The airplane is going to touchdown on the runway with wings level. It may still be slightly crabbed depending on the strength of the crosswind and pilot technique, but I'll still advocate it as being safer than a sideslip technique in most large transport category jets and numerous low wing corporate jets.


TP

 

[seagull]

It might be safer in most, but to say that "none of it matters" is not accurate. You are not on the ground yet, and depending on vehicle dynamics, there is still a lot going on, so for the case of the MD-11 specifically, the increase in coupling might not be a smart way to go.

 

[seagull]

OK, so the answer is that MDC based the procedure on what the autoland did. As you can imagine, designing the autoland to do a "decrab" maneuver would be challenging so it is either designed to land in the crab or transition into a side slip. In the case of the MDC they did the latter, transitioning to a sideslip at 150'. It was felt that having the pilot procedure aligned with what the autopilot did would be the best approach, so that is what they did. I am sure you can see the logic behind that approach. The reason the autopilot transitions at 150' is because doing it a bit earlier is easier for the pilot, if that is what you are going to do. The decision was made by the test pilots on the project. For the record, the landing gear on the MD11 and 10 is capable of handling landing in a crab up to the maximum limit. Also, all of the FCOM guidance that could be found from the DC9 onwards was for the side-slip method, so the discussion previously on the 717 must have been based on a company modification to that, not what MDC/Boeing had recommended at the time.

 

[BobDDuck]

The 717 goes in to "parallel rudder" around 1500 feet if I recall (we aren't authorized for autolands in the plane so Ive dumped most of this) and keeps the nose aligned with the runway. This jives with the MDC side slip guidance being based in the auto land system. It's not an overly comfortable approach to slip from there, but it does work. In the sim anyway, the landings are pretty smooth.

 

[SlumTodd_Millionaire]

The 717 goes in to "parallel rudder" around 1500 feet if I recall (we aren't authorized for autolands in the plane so Ive dumped most of this) and keeps the nose aligned with the runway. This jives with the MDC side slip guidance being based in the auto land system. It's not an overly comfortable approach to slip from there, but it does work. In the sim anyway, the landings are pretty smooth.

It's a shame that you guys can't do autolands. The airplane does them almost flawlessly. Makes the 737 seem almost defective.

But parallel rudder is a bit different than what you're thinking about. You're thinking of the ALIGN Mode, which doesn't happen until about 100 feet. Parallel rudder engages at 1500 feet in case of a go-around so that it's there for a lost engine, but the airplane doesn't align with runway until almost in the flare. It keeps the crab in until then.