Learning Experiences

April 2004 Issue




Mechanic’s Lean

“The new shop made the right call based on the information in front of them, but add in the information I had and it added up to something else.”

We had our 172 with its trouble prone O-320 cam shaft taken care of at a highly regarded shop located on the other side of the state. Following Cessna Pilots Association recommendations, we had the lifters pulled and inspected every 100 hours.

The shop called up after the last lifter inspection and said that the lifters were starting to show some wear and we should plan to just replace them the next time. I asked, “Why not now?” but he said the next cycle should be soon enough.

Our next oil change had to be at the local shop due to weather. There was a small amount of metal in the oil filter. I asked our main shop again if we should put new lifters in but he said to wait for the oil analysis and do a short oil change to look at the filter again. The oil analysis came back normal. With the holidays and unexpected good weather, we put a few more hours on the plane than expected. At this point, our main shop abruptly closed due to changes in the owner’s personal life.

The filter cut at the next oil change showed a smaller amount of metal. The mechanics looked at it and concluded again that the amounts were normal for a mid life engine and the plane was put back in service. I thought about the last report on the lifters, the fact that the few metal particles we were seeing were magnetic, and the sudden appearance of metal after nearly 1000 hours of clean filters. I called up the shop and said I wanted a whole new set of lifters put in as soon as they could be obtained.

Two days later we pulled the lifters and found the No. 2 and 3 intake lifters, which run on the same cam lobe, badly battered with small chunks missing from the corners. An inspection of the cam confirmed what we already knew, the cam lobe was shot. The engine was soon in a crate and on its way to the re-builder.

The FARs say that the owner is primarily responsible for the maintenance, and this is a good example of why it should be that way. The new shop made the right call based on the information in front of them, but add in the information I was carrying in my head about the history of the lifter inspections and the sudden appearance of even a small amount of metal, and it added up to something else.

I also learned that you should sometimes follow your instincts, even when they go against the advice of an experienced and qualified expert. I would have put the lifters in when the wear was first seen and quite possibly saved us a $10,000 to $15,000 overhaul or repair. I’d been getting a lot of heat from my partners though about being too conservative on the maintenance and it would have been hard to explain a $1,500 lifter job that the shop said we didn’t need yet. It’s easier to explain a five-figure job that we now need but probably could have avoided.

This episode also shows the tough position the shops are in. The AD on this engine says the lifters must be pulled and inspected if there is metal in the filter. In print, that means any metal. Since there will usually be some metal in an older engine, that would mean pulling the lifters every oil change. Realistically, the shop has to exercise some judgment that isn’t explicit in the AD. Of course, if a lifter fractures and a plane goes down, that judgment will look very different to the FAA and a jury.

Since this engine was sent out after the last oil change to fly again, the shop is pretty happy that I took the initiative to bring it back so the problem was discovered on the ground. After all, they have a lot riding in that plane even if I’m alone in it.

It takes an engaged and knowledgeable owner, working with a good shop, to properly maintain an aircraft. If you are just sending it in, saying, “Do whatever needs to be done” and signing checks, even a good shop may not be able to keep your plane flying safely.

----------

Eyes That Cannot See
One night while proceeding home from Key West in a Baron for a commercial student cross-country, I used my flashlight to check the fuel caps after take off. Baron caps have been known to leak, so I make it a habit to check the wings for streaming fuel every time. This night was no exception.

The routine was to check the wings in climb, level off, cruise checks, and switch to auxiliary tanks and auxiliary fuel gauges. The Baron had a switch to display either the main or auxiliary tanks on the fuel gauges. The auxiliary tanks were full and the fuel burn was normal.

On descent into Jacksonville, we switched the gauge to indicate mains before switching to the main tanks. To our surprise, the tanks read less than half full. Good thing we were close. We switched to main tanks for the landing phase and landed five minutes later.

Once we taxied in and beneath the ramp flood lights, I saw blue stains running down the wing, the result of streaming fuel. I know I had checked after takeoff.

As a full-time rescue helicopter pilot, I have the privilege to use some great equipment. Since we fly with night vision goggles, all of our flashlights are coated with blue-green lenses to shield the goggles from gain induced by the light.

I use the same flashlights when flight instructing in general aviation aircraft. Ever look for magenta symbols on a chart with a red flashlight? You will have the same luck checking for streaming fuel with a blue-green flashlight.

----------

Inadvertent Banner Tow
We are continuously reminded to do a complete preflight inspection. One spring day I was going to take my daughter on a scenic flight in the local area and rented a Piper Warrior for the flight.

As we approached the airplane, I sized it up to see if there were any obvious problems with it, but didn’t see anything. She was anxious to go, and so I felt the need to hurry through my preflight inspection.

We strapped into the Piper and headed for the runway. I guess I didn’t effectively use the checklist – although I did carry it around with me and looked at it. As it appeared I was approaching rotation speed I looked at the airspeed indicator and noted that it was reading zero.

Without hesitation I aborted the takeoff and taxied back to the ramp with the intention of blasting the FBO for not maintaining the airplanes in better condition. As I got out, I happened to look under the left wing and noticed the “Remove Before Flight” banner blowing serenely in the breeze.

Apparently my hurried preflight inspection was no better than none at all, and clearly I didn’t use the checklist effectively.


Other lessons to consider: The importance of checklist discipline is a great lesson to bring to the table. One other thing you might keep in mind is the “gauges green, airspeed alive” mantra you should repeat after you ensure the application of power hasn’t pointed you off the side of the runway. Waiting until rotation to check may put you in a position at some airports where you’ll run off the end of the runway if you try to abort.

Furthermore, learn to fly the airplane without the airspeed indicator. If the power is good and the airplane wants to fly, don’t let the indicator stop you if taking off is safer than aborting. Practicing airspeed inop landings occasionally will also come to your aid if you get pitot/static ice or otherwise cannot rely on the airspeed indicator.