Edgartown dentist Hélène Schaeffer thought she was being a considerate tenant when she notified the Martha’s Vineyard Airport Commission of plans to replace the roof of the professional building she owns on airport land.

Instead, Dr. Schaeffer was told that in order to proceed with the work, she must accept a lease amendment tying her rent to a fair market appraisal of the property.

“I’m shocked. I’m really shocked,” Dr. Schaeffer told the commission at its Nov. 9 regular meeting in the new Airport Rescue and Firefighting/Snow Removal Equipment building. “I’m questioning why fixing a hole is going to affect my fair market value on my lease.”

Under pressure from the Federal Aviation Administration to increase revenue, the airport commission in February adopted a policy in which the fair market adjustment is triggered when a tenant makes any significant improvement or modification to a property for which the lease has not yet matured.

“We’re trying to get everybody to be uniformly paying fair market value, and that has not been historically what has been going on here,” said commissioner Rich Michelson. “This is a policy we came up with to improve things at the airport business park and also come into compliance with FAA regulations.”

Some tenants in the business park are paying as little as 40 cents per square foot, per year, airport manager Ann Richart told the Gazette this week. The FAA considers such below-market rates to be a form of revenue diversion, which is strictly prohibited, Ms. Richart explained.

“Our appraisals have been coming back at $1.40 per square foot per year,” Ms. Richart said, adding: “I know a lot of people think it’s unfair, but when you think it through, it really, really makes sense: All airport revenue has to stay on the airport.” She continued:

“Revenue diversion is serious, and there are no exceptions to it.”

Any time an airport spends money on something that’s not airport-related, or even charges less than market rate for the use of its property, the FAA can call it revenue diversion and impose consequences for noncompliance.

These could include forfeiting capital improvement funding — guaranteed at a minimum of $1 million per year for the Vineyard airport, but often much more, as in this year’s $8.3 million dollar grant for the new fire and rescue building. In a potentially more severe sanction, Ms. Richart said: “We could lose our certificate, meaning we couldn’t serve commercial airlines any more.”

If the airport is unable to remain self-sufficient, Ms. Richart added, Dukes County taxpayers would be expected to make up the deficit to keep it operating.

While 40 cents a square foot may seem like a sweetheart deal, “it was nobody’s intent to get into this revenue diversion situation,” Ms. Richart said. “This was kind of a trick of the Island’s economy.”

When the business park opened about 20 years ago, she said, the standard lease rate was roughly 25 to 35 cents per square foot per year, with most tenants taking 20-year leases that usually included a 20-year renewal option.

“We did have a provision every year that we would adjust the rent according to the Consumer Price Index,” Ms. Richart said, but the result over time did not keep pace with actual market values.

“Anybody who’s done commercial real estate understands that CPI is a good adjustment from year to year, but over time that’s not a good way to keep track of property values,” she said.

The new lease amendment does not immediately catapult airport tenants to the fair-market level. Increases will take place over a three-year period following the property appraisal, Ms. Richart told the Gazette.

After the initial appraisal, leases will be again be adjusted according to the Consumer Price Index for four years with an appraisal in the fifth year, and so forth into the future.

In the case of Dr. Schaeffer’s building, which has 15 years left on its lease, there may be no rent increase for some time to come, but she remained unhappy about the process.

“I think I’m above fair market rate already, but it just doesn’t make any sense to me,” she told the airport commission.