Do we “bump down” these days? I was taught to land……
 

This was taken from another thread, quoting another user. But I was curious, How difficult is it to land a 737? or any 'large' commercial aircraft?

The landings always seem rough, but am told that particularly with the 737, you gotta put it on the runway quickly, without the need for a smooth touchdown?

Not a beat up, genuinly interested, are commercial pilots taught a smooth landing is important or does the plane need to be dropped onto the runway to keep it there?

Dog

i reckon the classic is easier to get a decent landing out of compared to the ng

I'm not too sure how they did it in the old days but there are the company stabilised approach requirements which can be 'policed' with the help of QAR's. Some one else may care to comment if they have noticed any changes in handling, speeds being flown etc. and has this had any impact on the apparent deterioration. For example the Dash seems to land so much nicer at Ref+10 and harder 'on speed', or maybe it's just me.

I can't speak for the 737 but I appreciate and comment if the bloke next to me flew the speeds, puts it firmly right on the 1000' marks and centerline of course:p . Anything else like 'mucking around' and floating looking for a greaser doesn't do it for me:rolleyes: .

Having said this, yes I'm guilty of bumping it on every now and then;) but when the greaser happens it feels fantastic knowing that I put it exactly where I wanted:) .

I close my eyes from 100' above...after all, "Any one you walk away from, is a good one!"

These sorts of professional secrets are VERBOTEN, dogi...so don't believe ANYTHING you read!! :E

In my book, you get far more points for touching down on the nominated spot (eg 1000ft markers) than you do for a "greezer" somewhere else. If you can get both together - good one!

Most accidents occur on approach and landing and many the result of not flying a stable approach according to well established criteria (FSF etc).

Any move away from flying the right speeds etc or trying for a greezer whilst floating well past the 1500ft marks is only asking for trouble. And if the Rwy is wet, then a firmer touchdown is the go.

I seem to find many pilots these days that don't have the basic skills or self discipline to put it on the spot 100% of the time. Something to do with training I believe?

Why?

It avoids aquaplaning

Oh really!!
And how does it do that?
Aquaplaning is a function of the square root of the tyre pressure, and will occur at an almost set speed on each aircraft type, regardless of how firm or otherwise the touchdown was, if there is sufficient standing water.....unless you figure you can make your "firm touchdown" at that speed.

What the passengers notice ?
 

If the runway is very long, much longer than "landing distance required", then I cannot see anything wrong in floating longer to make it a greaser, especially in an aircaft type difficult to "grease on".

Remember this very important fact :

The passengers (who keep the airline alive and pay our salary) can all feel the difference between a greaser and a thump,

but

the passengers got no absolute idea about touchdown zone markings etc,

Remember, some passengers are still very scared of flying and by making it a smooth flight followed by a smooth landing might encourage them to fly again one day or feel better about it.

Ill go with John Citizen on that one,

If landing distance avaliable is not an issue Ill always make an effort to grease it on with pax. Admittedly in my applications however it concerns light piston a/c only.

"Oh really!!
And how does it do that?
Aquaplaning is a function of the square root of the tyre pressure"

True when the entire weight of the aircraft is on the tyres. If a landing is "Greased" there is a period when the wheels are in contact with the runway, but the wings are still producing sufficient lift to support part of the weight. This has the same effect as a lower tyre pressure i.e. lower and wider range of speeds for aquaplaning.

Touching down firmly (a good idea at all times) puts all the load on the wheels and deploys the speed brakes in the shortest time, raising the the speed and shortening the range of possible aquaplaning.

By the way Kap,

How come you'll reply on this thread, but not on the one where you couldn't work out which decade an incident report was from?

I'm not sure if it'll do much about aquaplaning - not that I'm saying it won't I just don't really know - but placing the aircraft firmly down in the TDZ will:

*minimise risk of a float and associated increase in landing distance
*correspondingly minimise the time taken to speedbrake deployment and ability to actuate reverse thrust
*by reducing time to full speedbrake deployment, maximise the weight on the wheels sooner and therefore increase braking effectiveness.

My two bob's worth.

So if you want to make it a "greaser" then you have to "float down the runway" ?

If that is the argument, then why not aim for the 500' markers, float for 500' and "grease it on" at the 1000' markers ? surely this meets ALL requirements ?

Personally, my approach is to touch down on the 1000' markers AND try to grease it on. works most of the time, provided one remembers that Vref is the speed at which one should cross the threshold at 50' AGL, and not a touchdown speed!

You should be able to land smoothly AND touch down at the correct spot AND in a limiting crosswind, if you were trained correctly, and have some manipulative ability. IMHO the only pilots who advocate "firm" touchdowns are those who can't land properly or have no manipulative ability!
The training should have been done at abinitio, not on transition to heavy jets, as some think appropriate.:E

In my opinion it is a foolish driver who puts 'greasing it on' ahead of precision. Sure you should aim for the spot AND try to minimise the thud - in that order. Wizofoz is quite correct, a positive touchdown minimises tendancy to aquaplane on a wet runway, further to that (I was told by an old pilot many years ago) drawing out the touchdown or greasing it on increases tyre ware (delamination) - not sure to what extent this is true these days (better tyres) but it makes sense, the sooner the wheels are doing the same speed as the aircraft, the less rubber you leave on the tarmac - anyone else care to comment on the validity of this. Points about spoiler deployment etc are also valid.

By the way, I'm not talking spine compressing 'arrivals', just a gentle, but positive touchdown - ask Boeing or Airbus how their aircraft were designed to be landed!:ok:

FFS...a 737 is as difficult to land as a cherokee 6.

Whats the mystery?

Sure I'm not a pilot, but we were advised in good ol' ATC school - (I did the course at the now defunct Henty House, Melbourne) that weight of the vehicle had no bearing on aquaplane speed.

Aquaplane speed was a function of tyre pressure and speed, and that weight (or mass) of the vehicle had no effect. Hence, the advice to thump it down, because there was therefore more mass exerting force on the tyres would be incorrect.

We were also advised that to determine your aquaplane speed roughly (in mph), you take the square of your tyre pressure (in psi) and multply by 9. Hence if your tyre pressure is 25psi, your rough aquaplane speed is 45mph. Hence most cars will aquaplane at 80kph. I've managed to have it occur to me while driving through a large puddle at 90kph.

The reason we were advised about this using the old imperial measurements was because the film depicting the experimentation on aquaplaning was done by NASA. It showed a B1 thumping it down, then slowly drifting off the runway.

Tread pattern will make little difference, but grooves in the runway allow the surface water on the runway to drain quickly and help reduce the incidence of aquaplaning.

Correct me if I'm wrong, but I'm sure the info I received way back then is still correct.

Pierre,

you information is correct, but consider this...

the boeing documentation says that firm arrivals in the correct position are preferred over landing long and holding off for a greaser - tail strike being one consideration.

anyone who advocates landing long in order to get a greaser is on the wrong track in my opinion - but then I also disagree with Dash-8's landing long just because they can - it is most unprofessional in my opinion....

DHD, does this mean you were not of the brigade who used to land (just) on 03 at Perth with a touchdown about abeam Delta? ;)

I do notice the difference in the landings between a 737 and the 146. I've been doing a fair amount of commuting to Kal and Telfer over the last few months and the 737 landings always seem to be pretty positive, whereas the 146 just seems to trundle down onto the runway. Why is this?

But then again, sitting in the arse end of a 146 is a damn sight more uncomfortable (bouncy) than the 737 when cruising.:E

Dehavillanddriver,

I'm not certainly going to get into a debate about long, greaser, short and hot landings as this is outside my sphere of expertise (pity Dick Smith didn't do the same).

However, I must reiterate that weight of the vehicle has no effect on the aquaplaning speed, according to the experiments conducted by NASA. Whether the mass (weight) of your acft is partially supported by the lift of the wings, this should not affect the aquaplaning speed of the acft...according to the theory I was taught.

DirtyPiere,

You are quite correct - this applies once the wheels have spun up, untill then you must take rotational inertia into account - it's quite simple, the greater the mass of each wheel, the more it will resist 'spinning-up', and of course, untill it has reached full rotational speed the tyre is by definition hydroplaning or aquaplaning (even on a dry rwy - it's called reverted rubber hydroplaning) - instead of getting caught up in the formulae, consider the basic physics. The extreme example of this effect would be landing with the park brake on - does that clear things up?

Cloud Cutter,

I'll take your word for the effect of rotational inertia. I think the formula might be just a rough guide you can use to calculate aquaplane speed mentally. It certainly works for cars, and it doesn't matter the weight of the vehicle, whether you're driving a Ford F350 or a Fiat Bambino.

Please don't take my word for it, think about this - given your car example, that formula gives you a speed at which the car will hydroplane if you drive over a big enough puddle, if you put the anchors on, and give the wheels resistance to rotation, you can get the car to hydroplane at a much lower speed, particularly when your talking reverted rubber hydroplaning (when the surface of the tyre melts to form a liquid film) - this is essentialy a skid.

Huh??? You've contradicted yourself if you re-read what you've written, Wiz, notwithstanding that weight has nothing to do with aquaplaning speed anyway! (The contradiction in your "hypothesis, is on the one hand you are stating that during the initial touchdown the lesser weight on the wheels "has the same effect as a lower tyre pressure", then you go on to say this equates to " lower and wider range of speeds for aquaplaning.".
My impression has always been that the speed at touchdown is faster than it is towards the end of the landing roll.
Do you know something the rest of us don't, Wiz??

As Cloud Cutter has pointed out, speedbrake deployment is dependant upon main wheel spin up.

DirtyPierre, the formula of 9 times the square root of the tyre pressure to give aquaplaning speed (in mph) was always the one I had used as well, but I seem to recall reading (somewhere) recently that there was now more of a range (something along the lines of 7-11) with 9 still the median.
Anyone else seen this reference?

Cloud Cutter, rubber reversion is the phenomenom that occurs when the water trapped between the wheels and the runway heats up (to form steam) and dissolves the rubber into smallish tacky "blobs", further reducing braking effectiveness through the tyre to pavement contact. Well that was my understanding of it, at least.

Anyway, avoid speeds around 80-90 kph in your car on days when it's p!ssing down - I experienced aquaplaning in my car several years ago (by not following my own advice :zzz: ) and ended up off the freeway in a gully. It's a strange sensation, you can turn the steering wheel full lock both ways with just an index finger, and NOTHING happens....I just kept going straight ahead foot off the accelerator, at the SAME speed (until I hit the grass) :ouch:

My belief of the theory has always been to do with
the efficiency of the wheel brakes i.e to get the weight
of the aircraft on the wheels asap (hence spoilers)

If the runway is wet, a greaser will not deliver the
true weight of the a/c but an apparant weight significantly
less which in turn will cause the wheels to lock-up and
engage the anti-skid system which will, due to less
braking efficiency will increase the landing roll.

If Im completely wrong..so be it! :O

Put it on at 1000' whatever the conditions and if you stop / exit before the black stuff turns green, buy yourself a beer :p or better still get the FO to pay.

DJ737

The Roo Rooter :E :ok:

Kaptin M
Can’t see that that is one of the requirements for Ground Spoiler extension. Boeing might be different but the A330 FCOM 1 section 27 states that full extension of the Ground Spoilers will occur at landing if both main landing gear have touched down and:
· They are armed, and
· All thrust levers are at idle, or
· Reverse is selected on at least one engine (other engine at idle).

I have always been told that “greasing” it on is to be avoided, not because it increases the risk of aquaplaning but because it increases the risk of touching down outside the “zone”. If you know the runway is going to be slippery, it is best to get it on the ground, allow the spoilers to auto deploy and use full reverse thrust as these devises are most effective at higher speeds. Once the aircraft has slowed enough, the auto brakes with anti skid working should start to become effective. Obviously allowing the aircraft to float down the runway because you were after a “greaser” is a bad move in this situation and should be frowned upon.

It would appear that "bumping down" is still alive and well in a small town 300km to the east of Perth...

The local aviators (worried about avian flu these days I imagine) carefully "bumpdown" by the first or second wire on the runway... (oh, sorry, Rwy 10 doesnt have a cable arrester system, well what were you aiming for?)

Who needs a chiropractor after you have been shown a "bumpdown" reminiscent of Maverick in Top Gun (they all wear the glasses as well)... Even a chiropractor couldnt salvage what would be left of your spinal column...

It is rumoured that these pilots are so adept at "bumping down" that on many occasions they do this with such vigour that ones eyes retract in their sockets and end up somwhere around the anal region, hence the outlook achieved by many a young aviator in their employ...

If "bumping down" is an art, then they should all be bloody picasso... But then again, he put the one ear he had to good use...

404

How do you think the aircraft decides the mains are on the ground? On all the Boeings I'm familiar with, an armed spoiler pops up automatically when one of the wheels (eg 727 right main) reaches a certain RPM - of course manual deployment can be done at any stage but is usually not the norm. Sounds like the 330 may be different, maybe olio extension - but then, who know's with Airbus (donning flack jacket):}

Kaptin M, I know what you mean about the differing formulae for calculating the aquaplaning speeds. Apparently it is 7.7 if the wheel is not 'spun-up' and 9 if it is:) .

Cloud Cutter

I haven’t flown the B747-400 or the B777 but I have just looked up the relevant section of their FCOM 1’s and nowhere does it refer to the wheels having to spin up before the Ground Spoilers deploy. Maybe it is just a B727 thing or something? It make far more sense to me to have the Ground Spoilers deploy on a squat switch or reverse thrust when you are aquaplaning than on tire spin up which make not occur until you are off the far end of the runway.

Ground Spoilers B747-400 (FCOM 1)
On the ground, the Speedbrake lever stop retracts allowing the Speedbrake lever to be moved fully aft to UP position. All six spoiler panels on each wing extend to their full travel positions.
When the Speedbrake lever is in ARMED position, thrust levers 1 and 3 are near the closed position, and the main landing gear touch down, the Speedbrake lever is driven to UP position, extending all spoiler panels. If the Speedbrake lever is in DN position with the main gear on the ground and thrust levers 1 and 3 near the closed position, and reverse thrust levers 2 or 4 are pulled up to idle detent, the Speedbrake lever is raised out of DN detent and driven to UP position. This provides an automatic ground spoiler function for RTO and provides a backup automatic ground spoiler function for landing when the Speedbrake lever is not armed during approach.

Spoiler Speedbrake Operation B777 (FCOM 1)
In the ARMED position, the speedbrake lever is driven aft to the UP position when the landing gear is fully on the ground (not tilted) and the thrust levers are at idle.
The EICAS memo message SPEEDBRAKE ARMED is displayed when the speedbrake lever is armed.

Hey!...do we really need all this bloody hi-tech mumbo jumbo?

Everybody with their bloody ego hang ups trying to out-ego every one else with their super duper mathematical formulas about how to land a bloody aeroplane with a bit of bloody water on the bloody runway!

For crying out loud!...just read the bloody Ops Manual!!!

It's all there, you silly bloody Donkeys!! ;)

Kap,

Others (including yourself) with a greater understanding of this phenomina have made this a very educational thread. Thanks and I stand corrected on my misunderstanding.

This is known as admitting error-try it some time.

Amos,

If you have no interest in how Aeroplanes work, B***** off back to your fishing and but out of conversations between people who have something worthwhile to contribute.

Claret,

Yes I was the odd man out, and would land in the touchdown zone and taxi to the apron rather than hover taxi..

I was a big critic of the practice and was very disappointed that the check and training people in Perth actually encouraged it.

Um, Willy.........................that was Van Gogh!

It is more than two years since I left aviation, and I may be wrong, but I understood that, to have spoilers deploy automatically on touchdown of either Boeing OR Airbus, the following were necessary:

1. "Spoilers" lever to "ARMED"
2. "Weight-on-wheels" (squat) switch made
3. Both power levers at "Ground Idle" position

Spoilers will then deploy automatically, or have I got it wrong?

Kind regards,

TheNightOwl.

Well, the way I see it....everyone that doesn't know anything about flying (ie most pax) will always judge the skill of the pilot by their landings. So, if they fly with company X and find their landings a bit "firm" and then fly with company Y who grease em on....me thinks that they'll think that these pilots are better and will wanna fly with them.

I've got friends outside the industry that live by this rule....the better the landing...the better the pilot...therefore I'm flying with them always!!!

So, if runway is available and weather conditions ok, then why not grease it on? In saying that though if it's raining or there's crosswind or on a short runway then by all means a positive touchdown is the saftest option.

My two cents worth anyway.

"more than two tears since I left aviation" - Freudian slip there, TNO?

You are pretty much right - from the B737-400 Boeing manual

During landing, the auto speed brake system operates when these conditions occur:
- SPEED BRAKE lever is in the ARMED position
- SPEED BRAKE armed light is illuminated
- both thrust levers are retarded to idle
- main landing gear wheels spin up (more than 60 kts) - SPEED BRAKE LEVER automatically moves to the UP position, and the flight spoilers deploy
- right main landing gear strut compresses on touchdown, causing the mechanical linkage to open the ground spoiler bypass valve, and the ground spoilers deploy.

If a wheel spin-up is not detected, when the air/ground system senses ground mode, the SPEED BRAKE lever moves to the UP position, and all spoiler panels deploy automatically.

Umm, back on topic, (Surely you do more dry landings than wet anyway).....

If it is too hard to land decently, and you must dump it onto the runway.. surely you would need better training to land it decently on the right spot then? My dear old dad would never forgive me if i had that excuse doing circuits...