Undercarriage

[tom24]

At what point in the approach should undercarriage be lowered on a commercial airliner?

After a certain flap setting? Just before a certain flap setting? At a certain speed? At the point of GS capture? On base? At 4 miles? At 6 miles?

[T O G A Boy]

generally under normal operations, we use flaps 1 then 2 then gear down flaps 3 n then full. but sometimes the a/c is heavy and does want to slow down so we use flaps 1 then gear down to reduce the speed and then the rest. but on a fine day, we use flaps 1. as soon as the glideslope is alive( 1 dot) above capture, we use flaps 2. on the g/s* we use gear down usually 2000' agl. then flaps 3. then full.hope this answers your question....

[JW411]

The gear should be down and locked before touch down otherwise it gets horribly messy.

[mono]

On most large transport a/c the selection of large flap settings without the gear down and with the throttles at less than about half power will cause a warning horn to go off in the cockpit.

Helps to prevent gear up errors:ok: .

[Intruder]

After a certain flap setting? Just before a certain flap setting? At a certain speed? At the point of GS capture? On base? At 4 miles? At 6 miles?

There are several guidelines. From our 747-400 operations:

For an ILS, when the glideslope comes alive.

For a non-precision approach, about 5 -7 miles prior to FAF, so the airplane is in landing configuration before FAF.

"Gear down, Flaps 20" is normally a single call.

If Flaps 25 is selected with the gear up, the warning horn goes off.

[DrSyn]

You may have already deduced that there is no simple answer to your question, tom24. I will try to explain a few principles which ultimately revolve around a combination of aircraft type, economy, noise-abatement, traffic requirements and prevailing weather. However, although quite unusual in practice, and subject to limiting speed, nothing prevents the gear being lowered while the flaps are still retracted!

There is no standardisation in the nomencliture of flap settings across the various manufacturers and any settings given are only relevant to the type specified (as per the above post, but omitted by T O G A Boy). However, the basics are similar regardless of type. There are a progressive number of flap settings that can be used for the approach, beyond which warnings will sound unless the gear is down and locked (eg: On our 75/76s the normal approach sequence is Flap 1, 5, (Gear a/r*) 20, Gear DOWN, 30).

Most Ops Manuals state a height on finals at which the aircraft must be stabilised, that is, in the final landing config, on slope and track, on target speed and power set. This is often referred to as "In the Slot."

Due to its momentum and aerodynamics, a heavy jet such as Intruder's 744 needs a bit more airspace to decelerate and configure than does a lighter jet or indeed a turbo-prop commuter. It therefore follows that the slot for the 744 would be a bit further out from the runway than that of, say, the ATR-42. On our fleet we "should be stabilised by 1000' agl and must be stabilised by 500' agl" (about 3 and 1.5 nm finals, respectively). Most medium-heavy jet operators will have broadly similar rules.

Regardless of type, the aim is to fly the approach as far as possible at minimum thrust as this burns least fuel and thereby keeps both the company shareholders and the noise-abatement lobby happy. It also keeps you happy by retaining more valuable fuel for that unexpected go-around.

Remaining in the ideal world for a moment, most (turbine) pilots would fly the approach at idle thrust with an intermediate (approach) flap setting, then select gear-down and attain landing flap and stable approach power by the time they reach their slot on finals. On my types (and similar) this can be done at Flap 5 (or 20) down to a typical 1300'/4nm FAF at which point we initiate final config, commencing with gear-down, to achieve the in-slot requirements This equates quite nicely to a typical "Maintain 160 kts to 4 miles" instruction from ATC. Once in a while we actually fly into an airfield where this ideal occurs :)

Profiles in manufacturers' training manuals often show much earlier selection of gear, etc, such as glideslope alive, but this is rarely fuel-efficient or practicable on the line. In the UK at certain locations we now have constant descent patterns which, theoretically, are designed to avoid level-offs (and you get booked if you do!). As these patterns rarely bear any resemblance to our VNAVs, however well set up, it presents an interesting challenge - quite fun, actually ;)

In practice, air traffic requirements and weather conditions will require deviations from the ideal scenario. Because jets are designed to be rather slippery they are not very good at slowing down whilst descending. So if you are held high and/or fast during the intermediate approach you need to apply a bit/lot of drag at some point in order to achieve the slot. Speed brakes (spoilers) are generally helpful here but closer-in the gear is most effective at producing the desired drag and so it goes down early.

If you are in icing conditions on approach, the ice-protection system requires a minimum thrust setting, somewhat above idle, to function properly. Once again, the gear often goes down earlier to contain the speed. Likewise if the weather is particularly foul, gusty winds, tail-wind, lo-vis, etc, most pilots prefer to be stabilised further out than "normal" in order to avoid making configuration changes late in the approach.

Actually the list goes on, but I hope this helps to answer your question, tom24.

(*a/r = as required)

[tom24]

What an informative post DrSyn. It certainly does answer my question. More than what can be said for the childish response from JW411, the supposed TRI/TRE. Hope I don't end up ever being trained by him/her!

Cheers again.

[Jetdriver]

I agree that was an excellent reply from drSyn. To be fair though tom JW411s post, although not want you wanted, was I am sure a humerous reply rather than an offensive one.

You may well discover in your career that humour is a trait you will come to appreciate in the captains you fly with, be they training or otherwise. So be careful what you wish for.;)

[Busdrvr]

Tom:
From your post I can tell you, I would rather fly the rest of my career with JW411, than one leg with you. When you do make it to the stage in you career to interview for a position in an airline. They will be looking to see how well you play with others.

Also a good sense of humor makes a twelve hour day go by a little quicker.

Try to remember that. It might help you in the future.

[JW411]

tom24:

I have just read your response. I have to tell you that I get paid an awful lot of money for being "childish" and a "supposed TRI/TRE".

If you ever hope to get into professional aviation you will simply have to develop a sense of humour as a matter of urgency otherwise you will not make it through the first interview.

A good sense of humour and a strong undercarriage are just two essentials for ensuring a successful career.