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Is It A Matter of Size?


handyman
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Is it just me or have others noticed that the larger the aircraft the more careful crews are on the ground?

I have never seen a B747 or A340 taxi too fast or manouver in a manner which raised an eyebrow but I have seen a few B737's and A320's a little too fast. Last week I saw...ANOTHER...DH8 taxi so fast I'm sure it could have raised it's nose wheel clearly off the ground. Why is that? Is this attitude or complacancy part of the reason it is safer in larger aircraft? What have you noticed? ohmy.gif

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Guest 06L06R
Is it just me or have others noticed that the larger the aircraft the more careful crews are on the ground?

I have never seen a B747 or A340 taxi too fast or manouver in a manner which raised an eyebrow but I have seen a few B737's and A320's a little too fast. Last week I saw...ANOTHER...DH8 taxi so fast I'm sure it could have raised it's nose wheel clearly off the ground. Why is that? Is this attitude or complacancy part of the reason it is safer in larger aircraft? What have you noticed? ohmy.gif

A330 & A340 are usually slower than the rest. I have seen every aircraft type haul @#$ when on the ground. We just figure someone needs to go to the lav. B767 appear to be the quickest. They can really move it, I guess it it just a good aircraft to drive on the ground.

Both the DH8 and B190 repos really move fast some times. I have even asked them to slow down.

It can really mess you up when someone is going to fast or slow. I would love to see a set taxi speed where everyone unless it is an emergency drives at the same speed.

As for slow you can always tell when someone isn't ready to go. Just tell ATC and let the ones who are ready pass you.

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I have no data..... but I wouldn't be at all surprised to find it's only the size that gives a false perception that the smaller aircraft are being taxied any faster.

As was explained recently here, for one reason or another (?), the time it takes an object to move a distance equal to it's own length obviously varies with size.... thus skewing our perception of it's speed.

...but in general I haven't personally noticed any difference in care taken by size of aircraft driven.... I've seen both large and small skid a nosewheel in a turn. ...ferinstance... unsure.gif

Then again, maybe there's a grain of truth in what you say...? ...perhaps owing to the notion that it's usually crusty old farts like yourself driving the big ships.... too old, wise, and crotchety for any zippy youthful behaviour...? tongue.giflaugh.gifwink.gif

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There are a bunch of weight and size related factors to choosing a good taxi speed. Braking and brake temps, rough ride (sometimes it can get downright exciting on a rough taxiway at, say 15-20 knots) and turn planning are just a few.

The longer 340's (-500 and -600) present interesting turn geometry. Hit a tight turn too slow and you are going to need bags of power, too fast and you are going to either scuff a tire or clip some lights.

Something you might also be noticing is just the time it takes to accelerate or decelerate from a normal taxi speed. The lighter aircraft get to taxi speed almost immediately, whereas a heavy takes a long time to pick up speed at any reasonable taxi thrust setting. Likewise, it doesn't take much force to stop a light twin, but leaning on the brakes to stop a 340 is going to upset a lot of people and still consume a ton of distance.

FWIW

Vs

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Is it just me or have others noticed that the larger the aircraft the more careful crews are on the ground?

I have never seen a B747 or A340 taxi too fast or manouver in a manner which raised an eyebrow but I have seen a few B737's and A320's a little too fast. Last week I saw...ANOTHER...DH8 taxi so fast I'm sure it could have raised it's nose wheel clearly off the ground. Why is that? Is this attitude or complacancy part of the reason it is safer in larger aircraft? What have you noticed? ohmy.gif

Except when they clip another aircraft's wing. Is it just me or is this a bigger problem with larger aircraft?

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I think Mitch hit the nail on the head. It's purely perception due to the size of the aircraft.

Our SOP's allow us to taxi up to 30kts in the A340, obviously this can only be done in the right conditions. A dash 8 or 1900 doing 30kts on the ground looks pretty fast. Any dash drivers care to comment on thier taxi speeds??

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Yes perception could be a common problem but I have seen DH8's in YVR move so fast that one took a wrong turn and was well clear of the wrong taxi-way before ground could even respond. Luckily our towman stopped our tow otherwise it would have been "too close to call". I see no need for an aircraft to taxi greater than 30 knots...do you? dry.gif

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Guest prob30

I can speak for the 1900 only, but empty, with only the Captain on board (our SOPs allow for solo repo's), and only no-alternate-IFR gas remaining (625 lbs.) even in full beta the aircraft likes to taxi 20 kts. Leave it in ground idle and its more like 30 kts. Say it's friday night at 2000 hrs and...well, sometimes people get a little bit too eager to get back to the hangar...

Personally I think it looks like amateur hour when taxiing over 20 kts in an aircraft that size, not to mention those that like to taxi fast seem also to be predisposed to cutting across the ramp with no regard for painted taxi lines. 15-20 kts works great for me, and keeps the lateral G's to a minimum. biggrin.gifbiggrin.gif

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The Airbus SOPs on the A320 and A330 call for a max normal taxi speed of 30 kts. In addition, they recommend that if the aircraft is accelerating due to weight (or slope), that we allow the aircraft to accelerate to 30 kts, then apply brakes to reduce to 10 kts, and repeat. This is for optimal brake temperature and wear, but an even an A320 or A330 going 30 kts looks pretty fast.

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Not sure how you guys are measuring your taxi speed; the Dash I drive doesn't start showing speed until 50+kts! If I see that moving then I'd better be taxiing into a 50 kt wind. Taxi at whatever speed feels comfortable (within reason of course). I used to get told by folks on the ramp that they could tell it was me coming by the....ahh....quick taxi. Don't do that so much anymore (I think...).

Years ago when I did my multi rating, I was told by my instructor that if you're using brakes in a turn, you're going too fast. Kinda always stuck with me.

Doing the "one-engine-in-feather" taxi helps keep the speed down and save fuel.

I have to admit though, trying to keep up with Horizon while taxiing is a losing battle!

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Guest ACSideStick

Vanishing Point

The glass airplanes with IRS all display speed on the screen whether or not you're airborne. It's extremely accurate and updates instantly, and so is used to control taxi speeds. It even gives you the wind/direction readout as you taxi.

On larger aircraft, it really helps as the higher you are off the ground, the less your taxi speed is easily determined by outside reference. In the 320/767, you never take 90 degree corners faster than 12 knots (10-11 is preferable). Even in the 320, 25 kts seems slow and plodding. In the 767, 25 knots feels like walking speed.

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Vanishing Point

The glass airplanes with IRS all display speed on the screen whether or not you're airborne. It's extremely accurate and updates instantly, and so is used to control taxi speeds. It even gives you the wind/direction readout as you taxi.

On larger aircraft, it really helps as the higher you are off the ground, the less your taxi speed is easily determined by outside reference. In the 320/767, you never take 90 degree corners faster than 12 knots (10-11 is preferable). Even in the 320, 25 kts seems slow and plodding. In the 767, 25 knots feels like walking speed.

Yes, especially in reduced vis or at night. I have often thought I was slow and looked down at a GS reading of 25+ knots. For a 747, that's starting to get close to the limit of a safe speed especially when heavy and a long taxi. Tires tend to heat up real fast at that speed. ohmy.gif

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