Pumping the brakes puts pressure in lines?
 

Hi ppl,

One of the pilots here on the east coast of Australia told me that if I pump the brakes after my gear is lowered on my Cessna 210 then this will put pressure in the brake lines making them more effective when needed.

I didn't get around to asking him but how exactly does this work.

I understand that there is a master cylinder and when the pilot steps on the brake pedals then hydraulic fluid is used to squeeze the brake pads of the brake disc of the wheel.

But how does a few pumps of the brake when on downwind put pressure in the lines and then how does it stay there - I always thought that the pressure being applied by the hydraulic system was pretty much instant and now prior pumping was required.

Can someone explain further - many thanks in advance.

MK

So often people get funny ideas about the systems they operate and they talk nonsense. However, sometimes the ideas are based on an in-depth knowledge, that means they know more than the average person. Throughout my career, the tough part was sorting the good stuff from the cr@p It would be good idea to ask your instructor.

Does pressing the foot pedals release the parking / hand brake? This could be a reason for a test.

Maybe the pads get moved to the disc to take up the slack.

It may be that they are suggesting testing the integrity of the pressure line, by making sure the pedals do not sink to limits when foot pressure is applied. This would mean the fluid was squirting out and would probably only happen on one side. A fair piece of airmanship I would have thought.

If pumping the pedal did cause a permanent pressure rise, you're brakes would be on for an expensive landing!!

Aren't the C210 brakes separate from the gear operating hydraulics, though? I could be mistaken but I thought they were the usual Cessna independent foot motors with a 'pull and turn' handle for parking. Unless there's air in the system, the brakes shouldn't need pumping.
Steve.

Your instructor would probably be the last person to ask if you want technical facts. Sad to say but most wouldn't have a clue especially a newly graduated one who would only parrot what his instructor told him a few weeks earlier. Best read the manufacturer's POH. If there is nothing in there about pumping the brakes you can bet it is not needed. And if you don't believe me about the dearth of knowledge of some flying instructors, just ask them what is the POH recommended go around procedure and see if he can tell you word for word. You will be unpleasantly surprised at how little of the manufacturer's POH some of these characters know.

The only time you should need to "pump" the pedals is if the pistons have been forced back into the calipers. How you could do this in an a/c I have no idea, but it is often an issue with motorbikes that have suffered a "tank slapper".
However, on my pre-landing checks, I always pump the pedals to ensure that there is brake pressure when you need it. The last thing you want is to apply the brakes and have nothing happen, especially on a short runway...... If the pedals are soft during the pre landing check, then at least you have time to make a decision rather than when the boundary fence is coming up at you at a rate of knots.

pumping the brakes on downwind does nothing more than check for even pedal feel (pressure), and to remind you that the handbrake is off. in your 210r, it also reminds you that the gear is down and locked - what does BUMPFL mean again?

The only time I have come across this practice was at a certain FBO in the US, where it was SOP.

The reason was that if there was no pressure in the brakes, a longer runway could be chosen and a touchdown at the start would mitigate the risk of an expensive overrun.

The FBO owner told me that his insurance company had indicated that they would consider refusing payment if brake pressure was not checked in the air, on the basis that an overrun was an avoidable occurrence.

This was in the LA basin, where there was a choice of very long runways within a few minutes diversion from base.

I'm not commenting on whether I consider this good practice, just relating the facts.

Testing the brakes in flight may do something or nothing, depending on the aircraft and systems. Some brakes are completely disconnected in flight or bypass, others employ snubber systems internally which stop the wheels when the weight is off, or during retraction, etc. In aircraft with a wheel inbalance, applying gentle brake after takeoff sometimes reduces vibration.

So far as testing before landing, you're accomplishing little. A poorly maintained brake cylinder may be bypassing, and may require several applications to get a solid feel. In this case, applying pressure prior to landing is of benifit. Otherwise, if the system is properly maintained, then you shouldn't have an issue.

If one brake cylinder is weaker than the other, then "pumping" up both brakes by ensuring a solid feel may help prevent the aircraft pulling to one side on landing. Ensure if you're "pumping" up the brakes that you're not holding them, of course. If you're going to be landing in icing conditions, especially if you departed with wet wheels or brakes, applying brake may break ice which has formed over the caliper or pad area, and is sometimes benificial. Conversely, if you're departing such a location, allowing the wheel to spin and sling off moisture is also important, rather than stopping the wheel with the brake.

In any case, if you apply the brakes on a very short runway it will be done within seconds of touch down for obvious reasons. If the pedals go flat on first pressure you simply go-around and then reconsider your options. If you have landed on a long runway you probably won't need the brakes until you have almost stopped by drag alone so if the brakes go flat on first touch then there is no sweat. So - no point in "testing' the brakes before landing is there?

If one is performing a shortfield landing and equal braking action is a must for directional control, application and testing of brakes may be very important, depending on a variety of factors that include brake type and condition, temperature, meteorological conditions, etc. Just as previously stated.

Some aircraft have no ground steering capability but brakes; brakes are critical not only to getting stopped in such cases, but aircraft conrol. If both brakes do not apply equally during the landing, aircraft control may be lost; brake application prior to landing in such cases is often critical.

My instructor in the UK told me to check brake feel (ie pressure) on a Cessna downwind as the first step in BUMFLICH check.

My instructor in the US said he had never heard of such a mad thing.

so it goes ........

Seems to be a common thing for people to see their own lack of experience as a condemnation upon whatever it is that they may not understand.

Education.

I was taught that testing the brakes was a mandatory part of the pre-landing check. If you find you've lost the brakes a longer runway can be selected, or a divery to your alternative airport considered.

I think the "pumping up" the brake pressure issue is ahemmm "b0ll0x". If you have to do this get the plane into a hanger for some maintainance.

You're suggesting that an airplane in which the brakes might need to be checked or "pumped up" prior to landing is experiencing a malfunction or poor maintenance. Have you ever landed an aircraft which has no steering capability other than brakes on a short field requiring maximum braking right off the bat, and then had the aircraft attempt to go right or left on that narrow short little runway because one brake acted more effectively than the other?

Perhaps Because of air in the system, perhaps because two different actuating cylinders are used, each in their own state of wear, perhaps because of small differences in brake depth, or different temperatures of expander tube material?

Don't make the assumption that mererly because a cylinder may require or could use more than one application to ensure immediate response, that it's a sign of poor maintenance or even equipment condition. It may not be. In fact, it may be inherent to the type of brake. Some brake systems intentionally leave air in the assembly for expansion purposes, and may require an additinoal application to ensure response. Ice present on the disc assembly may need to be broken. Cold weather may mean a different rate of bypass or different sealing properties in the cylinder or different movement properties on the brake puck.

Do you know for certain you're "testing" the brakes when you apply them? Some systems bypass once the weight is off the wheels. How well do you know your system? If you're flying a cherokee, then you've got direct pressure between each cylinder and it's respective brake assembly...very simple, but you can still experience a difference in feel and pressure between them. This can be especially true if one has experienced a malfunction and been replaced with new, when the other hasn't. This doesn't necessarily mean poor maintenance or equipment, or a need to visit the shop. It may mean, operationally for you as the pilot, the need to ensure equal functioning prior to landing on a narrow short runway if braking and directional control may be issues.

Conversely, if you have a leaking brake or hydraulic system, pumping may mean you're pumping the last of your fluid overboard. Use care.

What on earth is a BUMFLICH check. Sounds a gay movie?

Well, certainly not into Gay Movies:) but how about an intelligent guess from a pilot?
Brakes
U/C (Down and welded...?:) )
Mixture
Fuel
L??? (Lights?)
Instruments
Canopy/Carb Heat?
Harness

Intelligence now drained:), but 'Prop' missing? ('BUMPFLICH'?), plus a few others....

Not the checks I used to use (sad to say I cannot recall them:confused:) but they'll do.

Let's see now:
Brakes? No requirement in the before landing check to check brakes in the Cessna 150/172 manufacturer's manual.
Undercarriage. ditto. Seems silly to confirm gear is welded down unless by mistake you happen to have taken the wrong aeroplane.
Fuel? Ditto. That is a constant airmanship thing not specific to before landing check.
Lights? Ditto. Nothing to do with landing.
Instruments? Ditto. Nothing to do with landing as you scan the instrument panel most of the time when flying.
Canopy? Ditto. If the doors were open you would certainly have been aware of it a long time before landing. Even if the doors were unlocked it makes no difference to the landing anyway.
Carb Heat. Yes - on. Now that is a valid check.
Harness? Yes, ensure it is on. Also you must confirm your fore and aft seat locking is engaged

There are so many superfluous drills and checks taught to unsuspecting student pilots that no wonder you need a whole dictionary of mnemonics to remember what they are supposed to represent. I know one flying school that insists its pilots use PPUFF checks before landing. Those letters represent Power Poles, Pitch controls, undercarriage, flaps, and furry and feathered friends. And the instructors actually teach this errant rubbish.
My recommendation is that you obtain a copy of the manufacturer's Pilot Information Handbook and use those drills which are professionally written by company test pilots.

Well, old bean - only trying to explain post#11, you know - not my checklist. I understand yours is
C
H
S
?

Maybe with a few more types 'under your belt' you will recognise the sense in having a 'standard' checklist so you don't miss that VITAL thing, like brakes in a Chipmunk, Fuel selector in xxxxx, DI at a multi-runway airport (to avoid that a w f u l feeling of lining up on the wrong runway:eek: ), Lights on in a busy circuit, maybe canopy open in a warbird, gear down in a retractable (or wheels up in an amphib), etc etc. Glad you agree with Carb Heat. Maybe there should be two F's (flap?). Who knows?

It can save a red face or worse, and I would advocate similar if sproglet is likely to move off Cessna 150s:ok:

It's precisely those kind of checks that keep the accident level so low. If anybody needs them it a single pilot flying alone and there are ever enough checks for that type of flying. You also should consider that the checks are also for the safety of the passengers as well who may not be as familiar with 4 point harnesses or the aircraft door locks.

And speaking as one who has consulted on and written many of the manufacturer's checklists and procedures in the AOM, FCOM and QRH, I know I wouldn't be comfortable with any operator who relied solely on those alone and hadn't considered the specifics of there own operation in their use. In fact if you read the AFM or FCOM closely I'm sure you'll find in most of them words to that very effect. Generally speaking, they're the minimum checks and procedures required.

Goodness me what a palaver I seem to have started with BUMFLICH !

BOAC has of course got it pretty much right.

A37575, I guess you don't have a PA28, otherwise you would recognise F Fuel as definitely a pre-landing check, fuel on fullest tank, fuel pump on. And L Lights, nothing to do with landing ? What are those big lights on the front of the aircraft for then ?

A quich look in Piper's POH shows all are there.