But there’s a limit to how much over the estimate an invoice can or should go before something has to give-either the shop gives you a break or, better, you knew the invoice was spiraling upward before the envelope ever arrived.

We frequently hear from owners asking what things should cost. “I had a cylinder replaced,” wrote one owner, “and they billed me $600 for labor, plus the cost of the jug. It came to $2000. isn’t that too high?” he asked. Without having the average time a mechanic takes to change a cylinder-a number we don’t expect to come by-we cant compare shop A against shop B or calculate any kind of average. Doing the math, at a $75 an hour shop rate thats typical in the shops we visit, it works out to eight hours of labor to swap a cylinder. That seems realistic to us.

Most owners report being surprised not by routine, known maintenance items like cylinder swaps, starter repairs or oil changes, but by novel items neither they nor the shop had encountered before. Oddball operations like rewiring a difficult-to-reach circuit or unusual sheet metal work can eat up the hours. We recently had a labor invoice triple and we rightly squawked, as most owners would. But should they? Is there an agreed upon standard escalation threshold in the industry where the shop is obligated to call the owner and report the bad news? Our answer to that includes the phrase, “don’t make us laugh.” Nonetheless, we circulated the question among various shops we know.

If there’s any universally appreciated quality that good shops have its that they notify customers when a shift in expectations has occurred. The labor will cost more, the parts will, the job will take longer or what the shop thought was the problem really wasnt. If the owners in the loop, there’s a far lower likelihood of an explosion when the invoice is handed over for payment.

“At what point would I call?” says Dennis Wolter, of Air Mod, a highly respected interior shop in Ohio. “If the job is going to run more than 10 percent over the estimate, you have an obligation to tell the customer,” Wolter says. “Its really more about communication than it is the dollars. You have to tell the customer what you found.”

Why more shops don’t adhere to this standard is frustrating, but its no mystery. Some people who fix airplanes are mediocre businessmen, but they may be even worse at customer service. The notion that swinging wrenches and schmoozing with customers on the phone belong in the same skill set is absurd. Further, some shops don’t have the staff to do customer outreach service, even if they would like to. And others mean to do it, but drop the ball with some customers.

The auto industry doesnt have this problem, at least not to the same extent. At the dealer level, the car industry is largely ruled by flat-rate pricing for practically every warranty and repair item imaginable. If you take your broken BMW to the dealer, the service manager will tell you replacing a fuel pump will take 3.5 hours at $105 per, plus $400 for the parts. (It is a BMW, after all.) And never mind that the mechanic-who might be paid both by the hour and the job-beats the rate and does the job in two hours.

The car factories have raised flat-rate pricing to such a high art that its pervasive enough to trickle down to even independent shops, which may charge a lower hourly than the dealer, but will still use the book guidelines to bill the job.

Nothing like that exists in aviation. For warranty support, the major manufacturers do provide service centers with flat-rate estimates for certain warranty service and some repairs, but nothing approaching what the car companies have. “It really doesnt cover much,” says Sportys Pilot Shop impresario Hal Shevers, of the Cessna flat-rate guidance documentation. He operates a Cessna dealership at Batavia Airport in Ohio. Basically, dealers report warranty claim activity, Shevers says, and Cessna pays the bills. The labor allowance is on the spare side of realistic, says Shevers, but only if the shop has done the operation several times or recently.

At least one of the major manufacturers, Diamond Aircraft, is expanding its flat-rate repair and warranty guidance to cover more items. Diamonds Gary Gaudreau, manager of customer service, says the company would like to describe fixing “every part that can break on the airplane” to give shops labor guidance.