How Much is Enough?

Some of the equipment on your plane can be broken without affecting safety, but some is absolutely essential


A student pilot was preflighting the cockpit of a Cessna 152, and as part of his routine, was checking the travel and friction of the throttle, mixture and carb heat knobs. Most pilots dont do this, but it was the detailed, deliberate and particular nature of this individual to check just about everything possible on the plane.

He was the kind of guy who would occasionally find himself the subject of some good-natured jokes from the other side of the FBO windows that faced the ramp, many of which were probably the result of a common, unspoken jealousy for a lack of a similar thoroughness. You can well imagine that the jokes came to a rapid stop the day he cycled the mixture from full lean to full rich to full lean – and had the entire mixture knob and part of the push rod come off in his hand.

Certainly you can imagine the first words out of his mouth, especially since he was getting ready to launch on his final, long student solo cross country. Sad to say, I do not believe he ever flew again.

This happened back in the early 1990s, when aviation had been mired in a slump for a decade. It was a time when the General Aviation Revitalization Act was still wet behind the ears. Cessna was talking about building the Skyhawk again, but the Independence factory wasnt even a dream. Piper was floundering in financial trouble and I was doing my crash-and-go circuits in the Cessna fleet of the late 70s and early 80s. The airplanes did their best, but you could not help but think that their best was behind them, slammed into a runway just one time too many.

One of these planes was the culprit of the above incident. Money was tight and all too often maintenance was loose. If the engine could turn and the wings could produce lift then, by golly, the plane was airworthy – at least in the opinion of the owner of this particular flight school. The owners of the planes on leaseback were a bit more vigilant, and to the renters, every little bit mattered. People would scramble to fly planes other than the ones in the school owners direct control.

Many times a pilot would have to crank an engine repeatedly to get it to start, and then it would come alive with such vibration and aggravation at being asked to work again that the plastic in the instrument panel would fall down onto the control yokes. Push it back up, give it a tap, wait a few minutes for everything to settle down, and it was time to taxi.

The radios, lights and intercoms were anyones guess. Nav lights? A joke. Everybody knows the FAA is home for dinner by 4:30, 5:00 at the latest. And if they do show up, well inspector, the light musta died after we started flying. Landing light out? Stick your arm out the window and use your flashlight. Instructors became pretty resourceful, both in making excuses and in salvaging lessons.

Signs of the Times
In retrospect, its amazing what pilots would tolerate in the way of maintenance discrepancies in the name of saving a couple dollars an hour in rental costs. Renters, of course, were at the mercy of the flight schools and FBOs that owned the fleets and managed the leasebacks. Owners had more control, but when they looked around the ramp the bar wasnt set too high in terms of aggressive maintenance plans.

Now that the economy is humming along, things are much better. Competition and the availability of dollars dictate that FBOs keep the planes in better repair than before. A few new planes are on the rental line. Owners find that springing for the popular avionics upgrades makes the rest of the plane look shabby, and adjust their maintenance budgets accordingly.

As a result, many of the annoying glitches are gone. Generally speaking, intercoms work, radios do not hum, lights light.

Even so, fleet managers and owners continue to dance around the question of what constitutes acceptable maintenance and, more importantly, what doesnt.

Most GA pilots tend to rely on common sense, especially with simple single engine planes. So what if a fuel gauge doesnt work? Youve always been told the buggers are unreliable anyway and you should fly by time. If an oil gauge is broken, though, most pilots would probably get it fixed. The information it provides is too critical to fly without it.

The Airline Call
Nowhere is the question of how close is close enough hammered home as strongly as in airline flying. When the FAA certifies an airplane, it does so based on the condition of the bird when it rolls out the factory door. Obviously the standards for a New Piper Warrior and a Boeing 777 are different, but the intent is the same. The FAA is giving its blessing based on the operability of the equipment on board; the manufacturer has put together a plane that has demonstrated it will work when constructed as planned, and that everything on board has demonstrated a minimum level of reliability.

Once the airliner is in service, however, the rules change a bit. Minimum Equipment Lists and Configuration Deviation Lists are compiled when an airplane enters service. The intent is to provide relief for the operators of the plane when something nonessential breaks. A good example is a coffee pot. When the plane is certified, the plane is deemed airworthy only if everything is working. But for an airline to cancel a flight because one coffee pot does not work is irrational and economically unfeasible. Therefore, the government and the operator set up a procedure for allowing maintenance deferrals of some items. In effect, the item is written up in the log by the crew, maintenance placards the item as inoperative, and the repair is deferred until a later date. A relatively simple and unimportant item like this might be deferred until the plane is in scheduled maintenance with enough time to get the problem fixed.

Other items, such as an engine generator, fall into less-clear territory. The Feds like to see at least two generators operating at a time. The twin-engine regional jet I fly is equipped with one generator per engine, with the auxiliary power unit providing a spare. A failed generator is fairly serious, but it can be deferred as long as two sources of electrical power are available. If the APU is already a deferred item, the plane is grounded. If the APU is working, then the deferral is made, the APU is kept running at all times and we are on our way. If the APU or the other engine generator dumps in flight, we land. Very simple.

The CDL is very similar to the MEL, except that it covers the outside of the plane, hence the term configuration. The most common is missing paint. For the most part, missing paint can be deferred indefinitely (there are a few exceptions), but if the plane is down for a long enough time for it to get done, it gets done. On our plane, aerodynamic sealant that seals the joints in the wings leaks at a steady rate, and it is common to defer it. It does, however, require 15 pounds to be deducted from our maximum takeoff weight. Missing gear doors cause a more substantial weight penalty. Static wicks? All but two are deferrable. Without em, we sit.

Each system on the plane is covered in the MEL or CDL. If the item is deferrable, and most things are, the conditions are listed. For example, one generator may be deferred provided the APU generator is functional and in use at all times. A code gives the length of the deferral (anywhere from 24 hours to indefinite). Any performance penalties are noted, as well as any necessary actions required of the crew (no night flight without navigation lights) or maintenance (collaring the circuit breaker of a deferred item).

If the item is not listed in the MEL, it is not deferrable. No questions asked. A common item is the third airspeed indicator or stand-by altimeter. In this case the aircraft may get a one-time ferry permit to take it to a maintenance base, but there are other items, like a shattered windshield, that absolutely requires grounding the airplane until it is fixed.

It may happen, however, that certain deferred items may be allowable according to the MEL and/or CDL, but dont quite feel right to the crew. This happened to me about a year ago, when I was a first officer. Neither the captain nor I were comfortable with the plane, and simply put, we, as a team, refused to fly it. Never heard another word about it.

Machine vs. Mission
For Part 91 operations, however, the judgment lies fully on the shoulders of the pilot. The pilot is charged with the legal responsibility for determining the airplane is airworthy, but also the practical job of determining if it is safe for beginning or continuing a flight. A broken autopilot may be deferrable for a short VFR flight, but you ought to consider at what point it is a necessity for single-pilot IFR with ceilings below XXXX feet. Define your own comfort zone to fill in the number. You can reasonably defer a burned out light bulb in the audio panel, but for how long? If the parking brake wont set for your preflight runup, you might make a case for deferring that, but only if youre sure the toe brakes arent also weak. What about that unreliable hand mike?

The point is that, for every system, every part, every nut, bolt, rivet, screw, seat, door handle, switch, seat belt and placard, there needs to be a point at which you, whether as renter or owner, will say, Enough is enough. Ill fly it when its fixed. If someone else wants to take it, fine. Let them. The odds are that most malfunctions in this gray area probably wont hurt them. But what would have happened to the Cessna 152 student if the mixture knob had come out in cruise over inhospitable terrain?

Determining what can be deferrable and for what period of time is something of a black art, but worth some effort. Make an inventory of your airplane some day when youre not even planning to fly. Write it down. That way, someday when youre convinced you absolutely must be somewhere, you wont be tempted to fudge the decision in a direction thats out of line with your personal tolerance for risk.

Start with the panel, specifically the engine gauges. They should all be no-go items because they provide critical information. These include oil temperature and pressure, volt meters/ammeters, tach – anything required in your plane by FAR 91 for VFR or IFR. Sounds like common sense, but people do dumb things all the time.

Fuel for Thought
A word about fuel gauges. Many people completely ignore them because of their famous unreliability in most GA airplanes. In fact, the certification rules require only that they be accurate in level flight when the usable fuel reaches zero. While this may seem like no help at all, it can be critical in those airplanes where you cant see the filler caps from the cockpit. So while you may not trust a gauge showing half full to actually be indicating that the tank is half full, if it falls to zero youd better do something quick. And if the gauge is always reading zero, get it fixed.

What about flight instruments? The VSI is the least important, so you might let it go. The altimeter obviously should be a grounder, especially for IFR pilots. In a Cub you might be tempted to write substitute two eyes, but theres that matter of equipment required by the FARs. Ignore at your peril. Attitude indicator, for the IFR folks, is again obvious. VFR pilots should at least cover it and up their minimum visibility to 10 or 20 miles, very high ceilings and no haze. Why? Why not? That margin will help to eliminate the possibility of VMC to IMC or getting stuck in hazy conditions that might be more than you can handle.

The point is, you need to sit in your plane and write down everything you have on the panel for instruments and radios. Then, you need to decide what you can fly with, and what you cant. See what guidance your POH offers. Ask your A&P. Ask other pilots, especially your CFI. Use the most conservative answer you can find.

If you own a plane that is on leaseback, consider your possible liability if a problem arises with a student, and it turns out that the problem could have been fixed with relatively little down time or cost.

As an owner, you have to have your bird inspected at least once a year. Can a broken seat back wait a year to be fixed? Id say no, but you may not agree. What about the missing static wicks? If the plane does a lot of IFR work, you may have two standards, one for VFR and one for IFR.

Whether you are a renter or an owner, go to the airport with a notepad and walk around the plane. Start big, then work your way to some of the smaller items. Write down those that stand out as possibly being safety hazards. Rate them from most to least dangerous if missing (or vice versa). Use the information readily available as a start. If you want or need more help, start making phone calls. Then, as you gain experience in dealing with broken items, you can make modifications to your MEL/CDL as you see fit, within your comfort zone.

Stick to Your Guns
Once you have your guidelines, stick to them as you would any of your personal minimums. Think about how combinations of squawks may compound each other. Think about how the kind of flight you are about to make fits with the weather and the condition of each system on board the airplane. Beginning flight with known deficiencies does take its toll in the accident record. The sad part about it is the accidents are almost completely avoidable.

Only you can decide what you can safely make deferrable, and only you can decide for how long youll put up with it. But never make the decision in a way that sacrifices safety, and never change your decision based on your need to get somewhere.

A last little bit: I was on vectors for an ILS to minimums in fairly hilly terrain when our ground proximity warning system started randomly calling out terrain warnings. We were able to silence the alarm before beginning the descent. Otherwise, we would have had to go someplace VFR. We wrote the problem up and the next flight took a substantial delay, but it did so in the interest of safety.

The fact is, its a rare day that you get on an airliner with absolutely nothing deferred. I have flown the turboprop in our fleet, a plane that is showing wear and tear, and I am currently a captain on our jet. Im lucky enough to fly a factory-new plane once a month, as well as the sire of the fleet. I had one with six hours on the plane when we had to write something up. It happens.

With more new planes entering the GA fleet, even at the rental level, we should all raise our expectations. MELs may not work on the fleet at every FBO and flying club, but you can have your own personal one. Use your common sense.

-by Chip Wright

Chip Wright is a CFII and ATP. He is a captain on the CRJ, living in Maryland and flying wherever scheduling sends him.


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