AirSpaceMag.com

Airplanes.

They are exceptionally durable machines, built of aluminum or, increasingly, composites. When properly maintained, they can provide decades of service. Commercial aircraft operated by airlines can last for hundreds of thousands of hours. Your car may give you 10 years, but after that it’s time to recycle it or ship it to Cuba.

The durable Beech Bonanza (flickr/Phil Ostroff)

Even the smallest airframes serve as reusable containers for new engines and electronics, upgrading as each new wave of technology washes over the stubborn structure. Wooden aircraft can rot, and aluminum can corrode, but both forms of decay can be kept at bay by care and maintenance. If that doesn’t work, there’s restoration and refurbishment. A Beech Bonanza, to cite one popular general-aviation airplane that typically is used heavily by its owners, will need an engine overhaul roughly every 2,000 hours. A smart owner will divide the dollar cost of an overhaul by 2,000 and salt away that many dollars in the bank for each hour flown as an “engine reserve” to pay for a new or zero-time engine when the inevitable replacement day draws nigh.

The virtuous durability of airframes became a vice when product liability lawsuits took off during the 1970s and ’80s. Manufacturers suddenly woke up to the fact that every long-lasting airplane represented long-term exposure to corporate liability in the event of a malfunction. After a long struggle, airplane makers were able to secure passage of the General Aviation Revitalization Act of 1994, which limited their liability to personal aircraft not more than 18 years old.

Although engines need regular attention, avionics are the best deal in the world. An owner can add them piecemeal or just yank out the whole instrument panel and replace it with technology such as that offered by Aspen Avionics: That company makes “glass cockpit” displays and systems that fit right in the old holes where the steam gauges used to sit, and it’s the very latest technology at an affordable price. Instant new airplane. And you don’t have to buy a new operating system every three years.

At small airports across the country, airplanes are handed down from one generation to another, not just as heirlooms but as real, live working modes of transportation.  We’ve all complained about the programmed obsolescence of our cars, our appliances, our computers.  Here’s one possession designed to last.

Slated for closure: the Wittman Regional tower in -- of all places -- Oshkosh, Wisconsin.

On March 22, an FAA press release announced the agency’s decision to close 149 control towers following the cutoff of funding more commonly known as “sequestration.” Outgoing transportation secretary Ray LaHood said the selection of towers for closing — all of them operating under contract — involved “tough decisions.” But in the aftermath of the announcement, there’s been little information about what effect the closings will have on flight operations.

Airports that have operating towers are designated as “controlled” fields. Those without towers are, simply, “uncontrolled fields.” Typically these are small rural airports, but they range in size from a single runway to former military bases with miles of paving.

FAA employees staff most airports that serve airlines and the traveling public, and those will remain open, although some may close at night when traffic tends to decline. The towers targeted for closing are staffed by non-federal controllers who work for private companies under contract to the FAA. In some cases, airports or local governments fund all or part of such a tower’s operation, and these towers too should be relatively unaffected.

How much of an effect will the closures have? Pilots of all stripes already follow established procedures for flying into uncontrolled fields. These procedures are spelled out in the Aeronautical Information Manual (formerly the Airman’s Information Manual) and are usually learned in the first few days of flight training, when the student pilot practices pattern flying and landings. If a tower is closed, inbound pilots would still tune in the tower frequency, transmit their position and intention to land, then follow that with continuing updates of position in the landing pattern; example: “States Air 43 is downwind for runway two-two, Metro Regional [Airport].”

At uncontrolled fields, pilots use a designated frequency — commonly called “Unicom” — to transmit advisories and monitor other nearby flights. An FAA spokesperson confirms that these established procedures will continue unchanged if the tower closures proceed with the first phase on April 7; the third and final phase is in May. Many airports are equipped with automatic weather monitoring and repeating transmissions that give pilots current conditions, and some also allow a pilot to illuminate the runway lights by keying the radio mike a set number of times.

Flight service facilities known as fixed base operators at some small airports voluntarily monitor Unicom and may even reply to incoming pilots with information about other aircraft known to be in the area. There are no plans to expand this service to actually control a field with a closed tower, however, probably due to questions about liability.

To sum up, the traveling public and operators of general aviation aircraft should notice little impact if the closures take effect. Pilots value the additional level of safety that tower controllers provide, but most will exercise additional caution and make good use of their radios.

Engineers who work in aviation learn to be risk averse. Change tends to happen slowly, through evolution rather than sudden breakthroughs. When a new idea comes along, it’s usually tested for years before being introduced to the fleet, and even then it usually debuts with the military—they have ejection seats, after all. Some engine components are tried out in ground-based turbines for electrical power plants before working their way into aircraft engines, a practice GE says it pursued for its latest engines.

One maxim of jet engine design is that higher power comes at a cost of greater heat. Unfortunately, heat melts metal. So anyone who can make an engine run hotter and still survive will be able to tweak more thrust out of the same amount of fuel. People have been working at the problem for years.

Somewhere in there is an ADVENT engine incorporating advanced ceramics. (GE photo)

Early in the game, engineers tried alloys that could survive the 2,000+-degree-Fahrenheit gas that meets the first set of turbine blades. But the gas, coming straight from the combustor, put such stress on the turbines that they only lasted tens of hours. The metal would soften to a point where the rapidly spinning blades elongated, and their tips began to rub against the tip seals on the engine’s outer wall.

By combining metals such as nickel, chromium and even more exotic elements from the periodic table, engines could be made to run hotter and survive. Later, the blades were made from crystals grown in such a way that the metal’s grain aligned with the centrifugal force, lending greater strength. Another improvement was cooling the blades with tiny passages that carried cold air to the leading edge, using air from the engine’s compressor to supply the cooling flow. That stole some power from the compressor, but the investment paid off in higher combustion temperatures and improved power and efficiency.

Research into the use of ceramics in the engine’s hot section began decades ago, starting with ceramic coatings on combustors and parts of the turbine section. A NASA technical memorandum (89868) dated May 1987, authored by Gerald Knip, Jr. at NASA’s Lewis Research Center in Cleveland, Ohio, describes “revolutionary materials” applied to subsonic jet engines. It describes ceramic composites that overcome the typical brittle quality of ceramics by using reinforcing fibers in much the same way that carbon fiber reinforces modern composites.

GE and the Air Force are now going all in with advanced ceramics, which are incorporated into a research engine called ADVENT for ADaptive Versatile ENgine Technology. In tests, the engine is reported to have run hotter than any engine ever built. Ceramic matrix composites, or “CMCs,” made from silicon carbide matrix and fibers, make it possible for the engine to tolerate gas temperatures of 2,400 degrees and achieve a reported gain in fuel efficiency of 25 percent. With fuel prices so high, that kind of progress, following decades of materials research, couldn’t come at a better time.