737 Question...

[91100 100 set]

Okay, so far nobody I have ever flown with has known the answer to this question. You know when you're sitting behind a 737 on the taxiway, and it looks "crooked", like it's always sitting at an angle, with the tail a few feet off the centerline even when they are rolling with the nosegear on the centerline? Why is that? I once heard a theory that the main gear trucks have a small amount of castor built into them. This kinda sounds like it could make sense to ease the sideload if you touchdown a bit crooked in a crosswind (can't drop the wing much and not scrape anything), but I mentioned this a guy who "was typed in the airplane" and he didn't know anything about it.

So whats the story?

 

[FlyChicaga]

Slight caster to the main gear. Just like you said, regarding crosswind correction.

 

[atrdriver]

I was told that the small amount of castering is built into the mains for the autoland system in a crosswind. Then, once it is down it holds that position until the weight comes off them again.

 

[D_G]

I never noticed it.

 

[ultrarunner]

It's prly all the old Ghetto Jets you're behind. I believe most of those are bent!

 

[FL717]

When I got my type rating, that was one of the first questions I asked. I had noticed for years that there is definitely a crab if you are looking at the B-737 from behind during taxi.

The interesting thing is that nobody I asked knew the answer, and our manuals make NO reference to this anomaly.

My personal opinion is that the theory mentioned above regarding a slight castor for crosswind autolands is the correct answer.

The B-717 will use the rudder to "ALIGN" during an autoland, therefore taking out the crab prior to touchdown. This is one of several features that allows the B-717 to be certified to perform single engine autolands, which we do at AirTran on the B-717.

The B-737 apparently could have this capability installed, but we do not have single engine autoland capability or certification on our AirTran B-737 aircraft, and don't know anyone else that does. Our manual simply states that in a normal (two engine) autoland, that a crosswind crab is normal and we are to "kick" this crab out when the autopilot disconnects on landing. It further states that the landing gear is capable of sustaining this crab... thus my unverified opinion regarding a slight castoring landing gear theory.

One final note... on the B-717, the aircraft "attempted" to track the localizer centerline on touchdown, however, on the B-737, when the autopilot disconnects after touchdown in a stiff crosswind, you really have to be proactive because it is NOT tracking the localizer centerline and you're very quickly "off to the races" in either direction.

Having transitioned from the B-717 to the B-737, I found that quite unusual at first.

 

[LarryinTN]

perform single engine autolands, which we do at AirTran on the B-717.

I hope you don't do them very often!

 

[FL717]

LOL!! I guess I should have worded that a little different!

The correct wording should be "which we are "authorized" single engine autolands at AirTran on the B-717".

I guess my budding career as a PR person is over before it started!

 

[TurboS7]

I know the exact answer to the question but it is imbedded deep into my harddrive. Midnight tonight it will come out. I know it is only on the 300/400/500/600 the 700/800 do not have the same gear.

 

[Swede]

AA's HUD 737's (and I think most HUD 73's) are authorized CATIII to normal minima. Of course these aren't autolands but the effect is the same, get it down SE in crappy weather.

Odd on the castor thing, I've never noticed it. Now I'll need to look for it.

 

[FL717]

I know the exact answer to the question but it is imbedded deep into my harddrive. Midnight tonight it will come out. I know it is only on the 300/400/500/600 the 700/800 do not have the same gear.

You're exactly right. In fact... the -700 and the -800 have the same gear, which is why a -700 sits higher than the -300. Put a -300 and a -700 side by side from a distance, I can only tell the difference externally by the gear height, and the "2nd" hole in the "tailcone" next to the APU exhaust, which is the APU compartment cooling vent. Its been a while since I taxied behind a 737, and do not remember in which model that I noticed the "crabbed" taxi. It very well may have been on a specific model.

AA's HUD 737's (and I think most HUD 73's) are authorized CATIII to normal minima. Of course these aren't autolands but the effect is the same, get it down SE in crappy weather..

At AirTran on both the B-717 and the B-737 we are/will be required to perform an autoland for Cat II and Cat III approaches. It seems funny listening to someone talk about a hand flown approach below Cat I, but you make a good point about getting down SE in crappy WX.

By design, this autoland requirement of ours forces us to look for us better WX single engine. Of course... there is ALWAYS Captains authority in an emergency, but to justify that there better not be a "suitable" airport at Cat I anywhere "close".

 

[ultrarunner]

What's the specific reasons sited for Airtran to be going with the extra expense of having an Autoland fleet. You guys gettin fogged out all the time?

Are SWA and JB doing autolands?

 

[FL717]

What's the specific reasons sited for Airtran to be going with the extra expense of having an Autoland fleet. You guys gettin fogged out all the time?

When I upgraded to Captain on the B-717, we didn't have any of the old B-737's left, and we had not gone out to bid on a new aircraft, so only the B-717 was considered in the Cat II/III decision making mix.

At that time the company was really pushing to get all the pilots trained in Cat II/III, because they believed that this would take advantage of the aircraft capability, and reduce some of the possible weather (low vis) problems associated with the ATL hub and spoke system that we relied on. As with most airlines (except SWA) when the Wx gets crappy at the hub, flight schedule integrity becomes non existent, and for a small airline like AirTran with limited aircraft and flights, it REALLY costs us $$$, and defeats part of the "Low Cost Carrier" plan.

Apparently when they got the FAA approval, it was predicated on Autoland Only approaches below Cat I, and this did not change when we got the new B-737's.

 

[ultrarunner]

Interesting. I had always thought that the training and equipment expense requirements outweighed any advantaged related to disruption of service.

Maybe that's not the case with a "smaller carrier".

thanks for the reply.

 

[calfo]

If you look at the scissors on the mains on a 737, you'll see a small hydraulic actuator that allows the gear to shift (I think) 2 or so degrees left or right. Our 737-700's didn't come with them at first and some of the crosswind landings were somewhat jarring. After the planes were fitted with the actuators, we can land sideways again...

 

[FN FAL]

It's prly all the old Ghetto Jets you're behind. I believe most of those are bent!

Don't laugh to hard...we just sent a Caravan back to Cessna. Seems they riveted the plane together crooked...it's been gone a while but I heard they had to un-rivet it and do some serious body work to make it right.