The Boeing 737 has a set of two wheels for its nose landing gear and two sets of two wheels for the main landing gear. This is a common layout for single-aisle planes, shared by the Airbus A320, for example. What isn’t shared with the Airbus, however, is how the gear functions. The main landing gear extends and retracts largely the same, but while the A320 has doors to cover the gear wells, the Boeing does not.

This is unusual because almost every other airliner covers its main landing gear doors. Look at the Airbus A320 or Boeing 757 for example. Furthermore, there has never been a widebody aircraft with exposed main gear wells. When the landing gear is retracted, the wheels are flush with the body, with a hubcap and rubber seal preserving aerodynamics. But when landing gear doors are a common feature on most other airliners, why does the Boeing 737 not include them?

Weight And Maintenance

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Contrary to popular belief, the low-rider stance of the 737 isn’t a factor here. The BAC 1-11, another airliner close to the ground, has doors for its main landing gear, as an example. But both the ground clearance and the lack of doors have a common reason. That is, simplicity. The 737 in its original form was designed to operate short routes to smaller, less developed 1960s airfields.

The idea was to make an aircraft as robust and as simple as possible. Being low to the ground made it easy for ground crews to service the plane. The aircraft lacking main gear doors meant that there were fewer items that could break. Today, it’s fairly easy for quick repairs to be made at most airports that 737s visit, but repairing a broken gear door at the airfields that 737s visited in the 60s would have been much more complicated. Instead, Boeing omitted them.

Additionally, landing gear doors do save some fuel as they’re more aerodynamically efficient, but they do add weight. The biggest fuel efficiency gains from the aerodynamic advantage would occur during cruise, but the 737-100 and 737-200 were strictly short-haul planes. It would have seen a very low fuel burn reduction compared to the gain that would have occurred from the added weight of the gears. With all of these factors, Boeinglet the gear stick out.

Building The Same Plane For Almost 60 Years

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The 737 was a short-haul plane for serving underdeveloped airfields when it was first unveiled, but that’s no longer the case. It’s now a huge mainline plane serving major cities that can seat 200 passengers and can even traverse the Atlantic Ocean. When Airbus made a clean-sheet single-aisle plane with cross-country capabilities, it included this feature. But the Boeing 737 program is almost 60 years old now, and adapting it to serve its new role comes with compromises.

Designing new airliners is hard, expensive, and time-consuming, which is why manufacturers often refresh their existing designs. Think of the Airbus A320neo, A330neo, Boeing 737 MAX, and 777X. But these companies must limit their changes, both to preserve the advantages of modifying an existing design and to ensure that the new variant can still be certified as the same plane.

Adding landing gear doors to future 737 variants would have required extensive reengineering work. This would make the plane more expensive to develop, and prices would increase. This also introduced the risk of challenges and possible delays. Any design changes also run the risk of not being certified, and could render the whole airplane as being considered a new type. Instead, Boeing kept its numerous redesigns easy and cheap, reaping the rewards in the form of thousands of trouble-free 737 Classic and 737NG sales.

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The Challenges That This Brings And How To Work Around This

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Landing gear creates a huge amount of drag, which is why airliners retract them into the fuselage. However, having the gear exposed partially reduces this benefit, since the underbelly is no longer a smooth surface. The weight savings help offset the fuel burn penalty, but this remains an issue. Boeing, however, does have a solution to this.

There is a small amount of space between the landing gear and the walls of the gear well. To close the gap, Boeing installs rubber seals on the bottom of the landing gear bays. This is a simple, low-tech solution that dramatically smoothens the underbelly. Furthermore, the wheels themselves feature large covers that again smooth the aerodynamic profile of the plane’s belly.

Although no doors cover the main landing gear wheels, the gear struts do have doors. These close onto the wing and the outer part of the belly. As such, only the wheels are exposed, and as previously mentioned, Boeing has made great efforts to clean this area up. The gear wells remain open during critical phases of flight, but Boeing elected to accept the drag penalty during these brief periods when the gear is down.

This Actually Isn’t So Uncommon

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This is one of the most eye-catching features of the 737, a notable difference from its Airbus rival. However, in the single-aisle world, this is hardly anything noteworthy. The Boeing 727 also had exposed gear wells, and so do today’s regional jets. Neither the Embraer E-Jet series nor the CRJ has landing gear doors. Even the Airbus A220, a modern short-haul aircraft has exposed landing gear.

As previously mentioned, landing gear doors add weight and complexity for the benefit of less drag. For short-haul planes, the fuel burn reduction is lower compared to a long-range airliner due to less time cruising. As such, many single-aisle designs lack landing gear doors. The DC-9 and its successors are a notable exception, as it was designed in the same era for the same role but featured doors. This shows McDonnell Douglas’s preference for aerodynamic efficiency versus weight reductions with the DC-9. This isn’t a wrong approach, but simply a different one.

You’ll only see this design feature on aircraft with one or two wheels per set. Aircraft that have more wheels utilize landing gear bogeys that are much more complex, and as such, cannot fit neatly into a space like the one on the 737. This is why the Boeing 757 and all twin-aisle aircraft ever made feature landing gear doors.

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Other Unique Features Of The 737

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The Boeing 737 is an interesting aircraft. It was designed in the 1960s, but new examples are still coming off the line in the 2020s. The Airbus A320 is a 1980s design, and many other aircraft still being made were either developed in the 1990s or after the turn of the century. As such, it features some rather distinctive quirks.

Its cross-section and forward fuselage are derived from the Boeing 707, a 1950s-era aircraft. It sits extremely low to the ground, an intentional feature back in the day, but one that has resulted in some distinctive characteristics today. The CFM56 engines have non-circular intakes for ground clearance, while the MAX’s CFM LEAP motors are practically level with the wings. The exit doors are smaller compared to an A320, and they swing open. This is more difficult for individuals operating the doors, and it likely wouldn’t have been approved today.

The 737 can get away with such features because the modern iterations still retain the 737 type certificate, meaning that these features are grandfathered in. Boeing only has to change what they want to, rather than having to meet today’s standards. Furthermore, these traits can come with benefits. For instance, the exit doors are lighter and less complex than those on newer airliners. The low stance, meanwhile, means that the aircraft doesn’t require exit slides in its wings, dramatically reducing maintenance costs.

The Rundown

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Since its first flight in 1967, the Boeing 737 has been reengined and redesigned three times. Back then, the 737 was essentially a larger version of a regional jet from today. Now, however, it’s taken the role of the old 727 and 757, becoming a large plane to serve larger markets. It does retain many elements of its original design, but it’s been reworked to fit today’s market needs, and Boeing has made use of the aircraft’s quirks, turning some into a benefit.

This particular feature, however, is not especially uncommon. Many planes that are newer than the 737 still incorporate this design element, largely for the same reasons. When you look at trends in the single-aisle world, what’s noteworthy isn’t that the 737 has exposed gear, but rather that the Airbus A320 doesn’t.