Ever wonder how airplanes are able to take off from and land on unpaved runways? Unpaved runways often contain small rocks or gravel. If an airplane has one or more jet engines, it may suck up debris such as this. Gravel kits are available, however, to allow airplanes to safely use unpaved runways.
What Is a Gravel Kit?
A gravel kit is an aircraft addon that’s designed to protect airplanes from gravel and other forms of physical debris on unpaved runways. It serves as a physical barrier between the airplane itself and the unpaved runway.
The Purpose of Gravel Kits
While the exact number is unknown, it’s estimated that there are roughly 6,000 to 8,000 unpaved runways in the United States. Many of these runways are located in rural areas where paving isn’t feasible. It can cost over $5 million per mile to pave a runway, so these small airports often leave their runways unpaved.
Unpaved runways, though, can damage airplanes if certain precautions aren’t taken. Foreign object damage (FOD) is one concern. FOD in the form of gravel can strike an airplane’s fuselage, wings or tail, causing physical damage to the respective structure.
Jet engines can also suck up gravel from unpaved runways. When this occurs, the airplane may sustain serious and costly damage to its compressor blade or other engine parts. Gravel kits protect against damage such as this by deflecting gravel away from the airplane.
Common Components of a Gravel Kit
A typical gravel kit consists of several components, one of the most important being gravel deflectors. Gravel deflectors are large ski-like metal shields. They are commonly found on the landing gear where they deflect gravel away from the airplane.
Airplanes with jet engines may have vortex dissipators as well. Vortex dissipators consist of small tubes near the inlets of jet engines. They release compressed air to disrupt air vortices that could otherwise suck up gravel and other debris.
Some airplanes have additional shields as part of their gravel kit. These shields are located on the underside of the fuselage. They may feature reinforced coatings that help to shield and protect the fuselage from physical damage.
What Airplanes Use Gravel Kits?
Not all airplanes use gravel kits. Rather, they are limited to airplanes that commonly take off from and land on unpaved runways.
Gravel kits are particularly common on Boeing 737s. Boeing, in fact, offered gravel kits as an optional modification in the late 1960s to its 737. With this modification, airlines and other operators could use the 737 at airports with unpaved runways.
