744: 180 Taxi Turns

[noblues]

Has anyone some tips on doing 180deg turns on limiting width runways in a 744?

ie. Close to the 46.6m minimum?

Visual references?
Entry Speed?
Differential Power and/or brake?
Turn into or away from a 'D' section?
Use full tiller lock straight off?

I've been on type for over 3yrs but still haven't done one for real, just know 1st time will be on some poorly lit runway on a dark wet night!

Thanks

[Carnage Matey!]

Latest Boeing guidance (IIRC) is align yourself as close as possible to the runway edge on side of handling pilot (we line up the edge in the bottom outside corner of the windscreen as guidance), bring aircraft to a stop, apply full tiller into the turn and use differential thrust and differential braking to complete the turn. Works very well in my experience, although initially feels a bit weird as it feels like the rear of the aircraft is going backwards!

[By George]

Once in the turn try not to stop mid-way around and keep 5 to 7kts going. Seems to work well although on a wet runway any paint markings, ie piano keys, will cause some slip with the nose wheel. MRU used to be a good one with two painted white sticks in the grass for reference! I still don't feel entirely comfortable doing 180's but the advice on the window ledge as a line up is spot on. It always feels like the wing gear is at risk but the Guru's say it's well clear.

[gas path]

Please try to avoid doing it when the body gear steering is locked out, it plays havoc with the oleo seals :=:8

[Intruder]

I would agree except for the "come to a full stop" part. It is MUCH easier to keep the nose tires "gripping" the surface if you ease the tiller initially while moving 8-10 kt, then put it hard over once the airplane starts turning. Lead with power on the outside of the turn, and tap the inside brake to help keep the nosegear from sliding.

If there's a "D" available, I start on the straight side of the runway, and use the "D" for overrun.

[Carnage Matey!]

The full stop advice came directly from Boeing and is supposed to be the best way to perform the turn on wet or slippery runways. Either way works adequately though and maintaining some speed into the turn helps avoid the use of higher power settings. Turning from straight side into the D is definitely a good idea.

[Intruder]

Do you have that Boeing reference?

With 10 years/5000+ hours on the 747 (both -400 and Classic), I have never been in a situation where bringing the airplane to a full stop helped to start a turn. Similarly, cranking the tiller full over while stopped is q very good way to start the nosegear skidding right off the bat, ESPECIALLY on a slippery runway! Tapping the brake is of greatest use when lightweight and/or aft CG.

Previous "Boeing" guidance that I heard in the past (for which I have also never seen a reference) that differential power should NOT be used has also proven to be misguided.

[Carnage Matey!]

Can't say I have the reference I'm afraid but we'd done the turns the way you describe for years until about 12 months ago when the procedure changed to the new 'Boeing' way and we all had to complete them as part of our sim check. I don't know why it changed but our trainers said it had come from Boeing.:confused:

[Intruder]

I've heard the "Boeing said..." claim too many times in 10 years to believe it every time I hear it. If the Standards guys can't come up with the document, it doesn't exist! Boeing just doesn't work that way!

[Carnage Matey!]

Boeing B747-400 Flight Crew Training Manual, section 2.8, October 31 2006. Knew I'd seen it somewhere. It relates specifically to when a minimum radius turn needs to be performed, otherwise you can keep the speed on into the turn.

[Flightwatch]

Extracts direct from the Boeing Flight Crew Training Manual - in this case dated December 2007. (My bold emphasis).

Intruder - Having been on the -400 since 7/90 and the Classic from 1984, now some 14,000 hrs later I can confirm that many techniques have been changed by Boeing over the years. It was certainly true that originally the recommendation in the FCTM was not to use differential power in a turn, (I can no longer give a reference, the pages have long ago been consigned to the bin), but then at first a 2 engined approach and go-around was performed on the -400 as in the Classic with very late selection of gear and flaps and continued descent on the glidepath to increase speed in the g/a whereas now it is done much more like a standard approach/go-around. The only way to keep abreast of all the changes is to ensure your company gives you a fully updated copy of the Boeing FCTM.



Ground Operations

Copyright © The Boeing Company. See title page for details.

2.12 FCT 747 (TM)

Approach the edge of the taxi surface at a shallow angle until the outboard side of the wing gear wheels are near the edge. The lower outboard corner of the pilot’s forward window is a good visual reference for the outboard side of the wing gear wheels on the same side. The lower inboard corner of the pilot’s forward window is also a good reference for the opposite side wing gear wheels.
Note: Painted runway markings are slippery when wet and during turns nose gear skidding may occur. Due to the area covered, wet threshold markings typically cause pronounced nose gear skidding during runway line-up. In these conditions moderate differential braking may help in turning without nose gear skidding.

Turning radius can be reduced by following a few specific taxi techniques. Taxi the airplane so that the wing gear tires are close to the runway edge. This provides more runway surface to make the turn. If maximum turning capability is required, stop the airplane completely with the thrust at idle. Hold the tiller to the maximum steering angle, release the brakes, then add thrust on the engines on the outboard side. Only use the engines on the outboard side of the turn and maintain 5 to 10 knots during the turn to minimize turn radius. Light intermittent braking on the inside main gear helps decrease turn radius. Stopping the airplane in a turn is not recommended unless required to reduce the turn radius. As the airplane passes through 90° of turn, steer to place the main gear approximately on the runway centerline, then gradually reduce the tiller input as required to align the airplane with the new direction of taxi.
This technique results in a low speed turn and less runway being used. It does not impose undue stress on the landing gear and tires provided the wheel brakes are not locked during the turn. If the nose gear skids, a good technique is to apply the inside wheel brake briefly and keep the airplane turning with asymmetric thrust as needed. If the turnaround is planned on a surface significantly greater in width than the minimum required, a turn entry could be made, without stopping, at 5-10 knots speed, using intermittent inside wheel braking and thrust as needed. Wind, slope, runway or taxiway surface conditions, and center of gravity may also affect the turning radius.

[Intruder]

Thanks!

I don't know where the "stop the airplane completely" recommendation comes from, because I can attest from experience that a heavy airplane does NOT maneuver easily from a stop, and that the brake-tapping technique for the inside brake is not very effective from a complete stop, even when light.

It certainly would be interesting to query "Boeing" on the source of the recommendation...

[Flightwatch]

Intruder,

As it happens I agree with you. However there are many strange recommendations given by Boeing hat seem to have no rhyme or reason. For instance pre-flight they require that in the before start procedure all fuel pumps in tanks containing fuel (with certain exceptions for the centre tank) should be switched on even with equal main tanks, with the cross feeds open. Then having checked the upper EICAS if the message "FUEL TANK TO ENG" is displayed then the overide pumps should be switched off and cross feeds closed. This despite the fact that if the cross feeds have been opened in the set up as required there is an advisory "X FEED CONFIG" clearly indicating that the main tanks have an equal amount of fuel in them and do not require the crossfeeds (and therefore overide pumps) open/on. Net result undue wear on the switchlights and overide pumps.

At my previous operator (a launch customer, I suspect Carnage Matey works for them) many Boeing SOPs were ignored in favour of more logical procedures - there was a very large and professional technical department looking after things. An example was that after a few years the procedure of using symmetrical reverse thrust on an RTO or engine-out landing was abandoned and the drill was to use all available reverse thrust. This then gave maximum stopping capability when needed and certainly in the simulator the aircraft was quite controllable even on a wet runway down to 80 kts. with max reverse on one side - what difference to a 2 holer with one out? I do not know if they have fallen into line now, it is 7 1/2 years since I left!

However I am lead to believe that in order to differ from Boeing a difference had to be declared to their technical department which meant they took no responsibilty for the consequences of the differing actions. As a result my present operator have gone for Boeing procedures both technically and operationally - the later with unfortunate consequences for co-pilots who apart from physically flying the aircraft when operating the sector are relegated to the role of system operators with little decision making to do. Of course in practice this may vary due to the requirements and application of CRM but for instance they do not taxi the aircraft.

I can only assume that Boeing have gone for the procedure requiring the greatest commonality between their types, in the above scenario many 737s do not have a tiller on the right hand side so rather than make differences between types they factor it down to the lowest common denominator.

Sorry for the thread drift - not much to do with minimum turning radii, I know.