Parking Brake

[n3833v]

Was there a part # for the swap outs or cyl specs to compare. A-S has cylinders, but other numbers. The parts sheet numbers [95-3681 or 95-3676] don't cross.

John

[ron74887]

well after 33 years of ownership I disconnected mine last evening after reading all this. The left lock lever had a U-shaped flat spring with 2 little feet to hold down the lock to keep it from jumping up and locking and the other had no spring. I remember the little coil spring that the parts manual shows at some time earlier when?? . Maybe I just saved my plane from a dishearten grave/ending/maintenence. I've never had a problem that I could blame the brakes on except one high speed turn off and the left brake may have been slightly engages cause I could not stop the turn. no damage but it never happened again. Checked the brakes an all worked fine, so left it alone--tTIL this thread .. Worth all the discussion!!! thanks guys. Ron

[lowNslow]

Mike Roe just PM'd me reminding me about another old issue regarding brakes. The 170 Book and the SRAM both talk about the failure modes of the serrated shafts on brake cylinders. All you guys who have the serrated shafts on your master cylinders need to start budgeting to get rid of them. They are failure prone, and should be swapped for smooth ones. (Simplest is to swap the entire cylinder.)

Not sure what you mean by serated shafts, what do they look like? (note: resist urge to write something kinky)

[GAHorn]

Take a look at the operating rods which come out the top of your master cylinders. The early "serrated" shafts have regularly spaced "notches" in them designed to engage the parking brake locking lever. These shafts break because of the machined notches.
The later cylinder operating rods are smooth, and round.

[lowNslow]

Thanks George, I've never seen these but what you discribed is what I invisioned.

[voorheesh]

Update. Talked with my IA and another IA and their objection is not that a parking brake is required or that removing it is a major alteration. My IA says he will remove it if I want and make a log book entry/placard the knob. Their objection is that it is not the parking brake that causes the problem it is the pilot. Yeh the parking brake like some other parts of 1950 era airplanes is primitive, but- say these mechanics- if well maintained is safe. My second IA friend has owned and flown Cessna 120s and 140s for years and his philosophy is to keep them "correct" and realize that the same risks faced by pilots in 1950 are not going away if we choose to fly these airplanes in 2008. (have you guys ever checked out the accident rate in the 50s?) My airplane has a relatively new interior and the parking brake is well maintained and adjusted. There is an argument that knowing about the dangers of applying brake in flight or on runway in a brisk manner could cause problems so we can avoid those by staying off the brake. So I don't know what I'm going to do except stop talking about it. If I do not disable the brake and ground loop some day, I will post pictures on this site and will have no one to blame but myself. I want to thank everyone for the advice including not to get thin skinned.

[GAHorn]

... My second IA friend has owned and flown Cessna 120s and 140s for years and his philosophy is to keep them "correct" and realize that the same risks faced by pilots in 1950 are not going away if we choose to fly these airplanes in 2008. ....

I would respond to your I friend: That's completely correct, as long as the airplanes are in the same condition as in 1950 you'll have 1950-ish results. That's why we have disconnected our brakes.... because we don't like the 1950 mod-standard statistics. The same logic would tell us to disregard every other thing we've learned in aviation for the last 58 years and not accept any safety education/advancements/developments.


It's your airplane and you get to decide for yourself.

[russfarris]

Voorheesh, I'm interested if your IA friend also has kept the Goodyear brakes on his 120/140s, in the goal of keeping it "correct". If the parking brake is not an airworthiness issue to him, it seems to be more of an "original" issue, since these airplane did come with Goodyear brakes and parking brake systems. I've enjoyed this thread, and appreciate your efforts to do things by the book.

I agree that if you never INADVERTENTLY apply the brakes in flight, you won't have a problem. But in gusty conditions, you might do that - and the parking brake system is there waiting...

As far as I'm concerned, this is a classic human engineering story. In this case, the engineers/mechanics feel that the system is safe, as long as the pilot doesn't do something dumb, like use the brakes in-flight. But, in the real operational world, it obviously can and does happen. In my case, I was taxiing in a high crosswind when I needed some downwind brake to stay on the pavement. The left parking brake hung up, imobilizing my airplane until I found the locking lever engaged. Landing in a high crosswind, I've had to use brakes to stay on the runway - good thing the parking brake didn't engage then. The Sun-N-Fun groundloop pictures George showed is what can happen.

This reminds me of a story about the Douglas DC-8, the classic airliner that was my first jet thirty years ago.

The original landing procedure back in the 1960s was to arm the automatic ground spoilers on short final. This involved pulling the spoiler lever up one click. On touchdown, main wheel spin-up moved the lever aft, deploying the ground spoilers.

In 1969, a DC-8 landing at JFK had the ground spoilers extend at about 200 feet when the first officer armed the system. They hit the runway with tremendous force, breaking the fuselage in two behind the wing. Fortunately, there were no fatalities. The crew was blamed for deploying the spoilers in flight, even though the F/O testified he only performed the one click arming action.

In 1970, an Air Canada DC-8 at Toronto wasn't so lucky. When the F/O armed the spoilers on short final, out they came... the DC-8 impacted the runway hard, tearing off an engine. The Captain, not knowing of the extent of the damage, went around. On the downwind leg the aircraft broke up, killing all 109 on board.

On investigation, Douglas, the MOT and FAA found that the spoilers could extend if even a slight aft pressure was placed the spoiler handle during the arming action. This was deemed pilot error - if the pilot would only arm the system properly, there wouldn't be any problem!

The initial "solution" was, I kid you not, a placard that said "WARNING - DO NOT DEPLOY GROUND SPOILERS IN FLIGHT" The joke at the time among DC-8 crews was the next placard required would be "WARNING - DO NOT CRASH AIRPLANE" ! Of course, it happened again, this time with less damage and no injuries. By now, most guys were deploying the spoilers manually on touchdown, regardless of what the FAA, Douglas and the airlines were saying about using the auto-spoiler system correctly and those careless pilots. Real world experience and common sense with this flawed system prevailed.

Finally, by the late 1970s every DC-8 had been modified to make deployment of the ground spoilers inflight impossible. What makes this relevent to the 170 discussion is that the Air Canada flight was landing on a gusty, turbulent day - a hard bump at the wrong time arming the spoilers probably contributed to the inadvertant aft movement of the spoiler handle, according to the accident investigators.

It's from a long time ago, but I thought it sounded very familiar...Russ Farris

[voorheesh]

The IA I mentioned no longer owns an airplane and I do not know what kind of brakes he used. The issue raised in this discussion concerns what I call a "stress" that has existed between mechanics and pilots since Charles Taylor and the Wright brothers began this business. It involves two very differing perceptions of airplanes. A pilot flies it while a mechanic inspects and maintains it. Both have undertaken rigorous training and certification and both are accountable for their decisions and actions. Pilots put themselves at risk flying and can get excited if something breaks or fails. Mechanics try and fix stuff and get excited if the thing still doesn't work despite their efforts which usually take place on rain swept ramps while pilots are asleep in comfortable hotels. Pilots have to deal with gusty winds and conditions that can change in an instant while mechanics follow manuals and perform tests and have much more time to evaluate and consider something before completing their task. You probably know this already but I'm trying to give you a flavor of what I am experiencing in my dealing with this parking brake decision. The people on this forum are mostly pilots and they are convinced this brake system is a plane destroyer. (I know some are probably pilots AND mechanics). I respect their opinions otherwise I wouldn't read this forum regularlly. My mechanic buddies who help me maintain my plane are from the A&P school and they just have that point of view that if "you pilots would just fly these things right, the world would be a better place etc. etc." In other words, to them, if I disconnect this brake I am a Wooss who is covering up my shortcommings. They haven't said that to me, but this is my perception. So I am in the middle of the stress and trying to make the right decision. I respect George and I am probably going to get it disconnected as we do this annual.
Regarding DC-8s, I suspect when that airplane was designed and certified its performance was a critical component in its initial marketing. As I recall the runways in the 50s and 60s were yet to be lengthened to accomodate the jet age and the manufacturers needed all the help they could get to meet the old 60% rule. The technology in that early spoiler system is analogous to the 170 parking brake: primitive and works well on paper. Its a real shame that people had to die to learn those lessons. I don't think the 170 parking brake carries that high a risk but the same principals apply.

[c170b53]

The DC-8's lasted longer than most thought they would. I stopped working on them in 1981 but the planes I maintained remained in service as cargo planes until they were finally scrapped in 2003. Keeping the airplane looking like it did when it was built is the goal of many here but in my opinion function must be the final safety consideration. In many instances with the 170, safety has not been the main reason to modify. Thats one of the reasons the 170 are valuable and sought after. There are always weak points in a design and both mechanics and pilots can recognize them once they have a chance to become familiar with the issues. It does take much imagination to see the potential for the little levers on the brake cylinders to act like the lock tab on your screen door spring cartridge. I can't see anyone beating themselves up over this one.

[russfarris]

Everytime I see a DC-8, I get a little lump in my throat. It's a great airplane; I spent almost 5,000 hours in them as flight engineer, co-pilot and finally captain. I can remember the limitations and procedures better than the Airbus 320 I currently fly. As a first generation jet transport it had issues, but it has outllived the Boeing 707, primarly being by re-engined with high-bypass CFM-56s and a simple DC-3 approach to major systems. Some still operated by UPS have over 100,000 hours airframe time!

Voorheesh, you touched upon a subject not often discussed...the void between pilots and mechanics. I have always had a good relationship with my buddies that help maintain N8143A to the high standards I demand. Part of this is because I'm pretty handy - I do my own work on my airplane, totally maintain myself two 1960s Studebakers and I'm certainly not afraid of getting my hands dirty! My IA is a pilot who has built two RV-4s, and was a crop duster, CFI, charter pilot and C-130 F/E. With his vast experience fixing (he's restoring a Great Lakes bi-plane) and flying expertise, I have the best of both worlds; an outstanding mechanic and a pilot who understands how what looks good on paper doesn't always translate to the real world. I'll probably get flamed for this, but I never use an AME or mechanic that isn't also a pilot. In my experience, non-pilots seem to think that their job description is to ground you...just an opinion. Flame suit on...Russ Farris

[1SeventyZ]

Risk vs reward.

There's not much risk in removing the parking brake, and not much reward in leaving it in, either.

There is risk in leaving it operational, though.

[GAHorn]

I am both a pilot and a mechanic. In my own view, I appreciate the fact that pilots are more artist than scientist. As a pilot flys, he makes many compromises in order to achieve the desired goal of the flight. He can realize that although there is black and white, that solutions may involve a little of both and that grey can be an OK color.

Mechanics are more scientist than artist. A mechanic does not like compromise and will resist any efforts to alter what he believes is, and should remain, a black or a white operation. He never wants to operate in the "grey".

Bill O'Brien is the national resource specialist for the Federal Aviation Administration in Washington, D.C. and also writes for AMT (Aviation Maintenance Technician) magazine. He wrote not long ago about the difference between mechanics and pilots, and how their differences affect their relationships and viewpoints and communications difficulties.

I don't agree completely (as most of you probably expected) but here's some of what he said, and a link to his article:

"Pilots are risk takers because flying is inherently risky. They like the fact that they are risk takers and they buy very expensive watches with many dials and knots that can calculate the orbits of Jupiter’s moons. For the most part the watch is useless in the cockpit but it is used as a risk-taker’s badge not to tell the time, but to identify to the world that he or she is in the risky business of being a pilot.

Mechanics are poor communicators. Aviation mechanics are for the most part closed mouth souls, who quietly go about their business of fixing aircraft. High school English was not one of our favorite subjects. I still don’t know what a dangling participle is. For the other attributes listed below mechanics do not have a burning need to explain themselves. Many of us find it hard to write a letter and if we must we deliberately keep it short and sweet.

Pilots are good communicators. Mechanics’ unobtrusive approach to spoken or written word is in stark contrast to the endless self-promoting repartee of our flying brethren. Pilots are in love with words and especially writing. Their most creative and inspirational writings are found justifying each trip’s expense account.

Mechanics are yes/no decision makers. If you really think about it, our whole profession is about yes/no decisions: It’s airworthy or it’s not, the plane goes to the gate or stays in the hangar, we have the part or we AOG it. This yes/no approach world we live in every day makes it almost impossible to compromise with people. How does someone deal with an individual who says: “What part of no don’t you understand?”

Pilots are compromisers. They have to be. I don’t know of a single pilot who believes he or she will fly the flight plan as originally written. There are always “pop ups” such as weather, ATC en route course changes, or mechanical problems that require a person who is good at compromises.

Mechanics are process oriented. We do things in steps: 1-2-3-4-5. This is how we are trained and this is how our maintenance manuals are written and heaven help the person who suggests that we start with step 3 before we have finished steps 1 and 2.

Pilots are goal oriented. The pilot’s main mission of each flight is to get there. Whether the flight is 100 miles or 10,000 miles, their destination is their focus. The process is always secondary to the goal. The pilots‘ secondary goal other than reaching their destination is to have the same number of take-offs and landings in their logbook."

http://www.amtonline.com/publication/ar ... =1&id=5572

If a parking brake on a 170 is properly maintained, then the mechanic feels safe in that he will not be blamed for the accident since he only maintained it in the mfr's approved method. It's either a mfr's error, or a pilot's error should it become engaged in flight.

I maintain that a pilot who knows a piece of equipment is defective either through wear, poor maintenance, or poor design, ... should not operate with that equipment until it is rendered safe by either good maintenance or alteration to a safe design. There are many, many examples in aviation history where defective designs were approved for flight by disabling the equipment. Other than the ash trays, I cannot imagine a less important piece of equipment than the parking brakes. I have kept my ash trays.

[n2582d]

It's always hard to prove that a problem occurred because of a parking brake that was unintentionally set, because it releases as soon as you touch the brake. For that reason I would be surprised if Cessna or the FAA would be able to confirm there was a problem with the design. (Note that Cessna did change the design in later aircraft.) One great value of an organization like this is the accumulation of anecdotal evidence -- the kind of thing the manufacturer or the FAA couldn't really act upon, but it still serves as a warning for the rest of us.

John,
I agree with you in that this organization is good as a clearing house for issues like this. On the other hand at times I believe it has the unintended consequence of preventing the wider dissemination of maintenance issues such as the parking brake. Mechanics that are not 170 specialists can hardly be expected to be aware of this potential problem on the 170. This is why the FAA came up with the Service Difficulty Program. Pilots who have experienced problems with their parking brakes inadvertently locking should file an SDR. It seems to me that if enough pilots had done this in the past the FAA would have issued an AD and required us to have the parking brake disabled.

According to this website
http://www.faa.gov/aircraft/safety/aler ... _Alert.pdf A report should be filed whenever a system, component, or part of an aircraft, powerplant, propeller, or appliance fails to function in a normal or usual manner. In addition, if a system, component, or part of an aircraft, powerplant, propeller, or appliance has a flaw or imperfection, which impairs or may impair its future function, it is considered defective and should be reported under the Service Difficulty Program.
The collection, collation, analysis of data, and the rapid dissemination of mechanical discrepancies, alerts, and trend information to the appropriate segments of the FAA and the aviation community provides an effective and economical method of ensuring future aviation safety.
The FAA analyzes SDR data for safety implications and reviews the data to identify possible trends that may not be apparent regionally or to individual operators. As a result, the FAA may disseminate safety information to a particular section of the aviation community. The FAA also may adopt new regulations or issue airworthiness directives (ADs) to address a specific problem.

[GAHorn]

SDR (Service Difficulty Reports) and Aviation Maintenance reports focus on problems found during maintenance as the result of mechanical failure or difficulty in making repairs to defective equipment. They do not address operational difficulties resulting from poor design.

A Cessna landing with a parking brake set would not meet the criteria for SDR/AMR's, and instead likely be assigned to the category of operational error - pilot induced.

The only reason a parking brake problem such as we have been discussing here might make it into a SDR/AMR would be if the pilot knew it was locked prior to landing and found it incapable of being UN-locked..... not a scenario likely to be encountered.