While watching a video today about airplanes and how they have little thingies on their wings to make them come to a stop much quicker than otherwise, I noticed something very odd: spoilers of a plane activated during landing, exposing wing internals

Are those cables and electronics? Just exposed right into the air like that? Isn't that bad? Sure, it's on the back side, thus not immediately facing the wind, but still, what if it's snowing or raining? It looks downright scary to me. Or am I seeing things? It's not the sharpest screenshot or video.

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    $\begingroup$ Yes, that screenshot is an accurate representation of exactly what you would see from that angle. Assume that every component on the aircraft, particularly those to do with flight control surfaces, has been engineered to the n-th degree over many decades of experience. $\endgroup$ Dec 29, 2021 at 0:35
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    $\begingroup$ Have you looked on the underside of a car? You will find hydraulic plumbing for the brakes as well as electrical cables. Below a car is a much worse environment for these than on a plane. And if we maintained our cars as well as the planes, the cars would last at least 80 years. $\endgroup$
    – ghellquist
    Dec 29, 2021 at 13:10
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    $\begingroup$ @ghellquist also, construction and farming vehicles covered in all kinds of hydraulic lines.... $\endgroup$ Dec 29, 2021 at 16:04
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    $\begingroup$ Also: Rain and snow is very pure water ... water splashing up from a road surface, mixed with grit, dirt and salts, is very likely 1000x worse ... $\endgroup$ Dec 29, 2021 at 16:06
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    $\begingroup$ I think this is an excellent question. We are not used to the inner parts of our safety critical machinery being open to the elements like that, so it is surprising at first. $\endgroup$ Dec 29, 2021 at 21:43

6 Answers 6


You will have both hydraulic system plumbing lines, the metal pipes, and wiring harnesses running along the rear spar, serving hydraulic actuators and electrical components like sensors and servos, etc.

The hydraulic plumbing is already hermetically sealed, being hydraulic plumbing holding 3000 psi (21 MPa), so being exposed is no big deal. The wiring harnesses running along the spar will be encased in waterproof sheathing, and the electrical connectors (cannon plug type generally) will be ones designed for exterior use with hermetically sealed back shells integrated into the harness sheathing.

It's a very demanding environment because the electrical components have to maintain their integrity while subjected to temperature cycles from surface ambient down to -60°C at altitude, plus pressure cycles. Any air leaks that allow the sheath or connector to breathe will pull water in as air is drawn in during descents as the pressure in cavities equalizes. Components in locations like that have to be designed to fully breathe, and withstand direct exposure to moisture, or else be hermetically sealed.

Water getting into the harness wire looms will wick up inside and corrode the internal shielding. Water getting into the electrical connectors will cause crosstalk between electrical circuits as moisture provides leak paths between pins, and you will get related system faults when voltages appear at pins that shouldn't. The weak points for water ingress are usually the boots that cover the back shells of electrical connectors, or the connector interface where it plugs into something.

The other items you will normally see are control cable runs for non-FBW airplanes, and obviously, flap system drive lines, which all have to be designed to withstand the exposed environment (actually more or less enclosed when at altitude, the exposure is only when flaps are down or spoilers are up, but they are still exposed to the pressure/temperature cycles).

You would think that you would use stainless steel control cables for these runs, but, at least in RJ world, only galvanized steel cables are used because stainless has less strength and doesn't like to rub against itself (the cable strands break down over time where the cable goes around corners). So one thing you have to inspect for during heavy checks is cable corrosion (rust) and pully bearings breaking down and seizing (especially horizontally mounted pulleys, as the grease slowly leaks out of the bearing).

The wing box forward of the spar is full of fuel, and to run that stuff through the tanks will require conduit pipes and result in poor access, so along the rear spar in the open is the easiest place to route all that stuff for ease of maintenance. But overall, keeping the moisture out of the electrical harnesses and connectors is probably the biggest struggle.

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    $\begingroup$ Good, comprehensive answer. As you note, the structural quality of the hydraulic plumbing is excellent. Some newer models of commercial airplanes (e.g., A380, A350XWB, B787) have 5000 PSI systems. Higher quality material for the plumbing allows the 5000 PSI systems to use smaller piping with a resultant overall a/c weight reduction. $\endgroup$
    – 757toga
    Dec 29, 2021 at 4:02
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    $\begingroup$ Thanks. Problems with wiring harness water ingress in wing TEs in service was the bane of my existence on the CRJ program. $\endgroup$
    – John K
    Dec 29, 2021 at 6:09
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    $\begingroup$ -60°C or -60°F? $\endgroup$
    – gerrit
    Dec 29, 2021 at 11:48
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    $\begingroup$ @gerrit "-60°C or -60°F"? at that point, not a whole lot of difference, considering that -40C and -40F are the same thing. $\endgroup$
    – Glen Yates
    Dec 29, 2021 at 15:29
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    $\begingroup$ The actual certification qualification temperature range on most airplanes is -40C, sometimes a bit lower. But the parts will be exposed to -60C at high altitudes in the winter. $\endgroup$
    – John K
    Dec 29, 2021 at 16:01

To complement things mentioned in other answers and comments, in particular the mention of the underside of a car, here is what the undercarriage well looks in a Boeing 737:

enter image description here

Neither these pipes and cables nor the ones in the OP, are continuously exposed to the elements, though they do during a landing. They are designed to do so, the same way that the underside of a car is designed to survive the water and little rocks that continuously hit it.

This question and its answers also provide more data.


You are seeing spoilers deployed at/after landing in order to reduce the lift on the wings and make the braking of the aircraft more effective.

The "cables and electronics" as you call them in your question are primarily high quality, adverse weather resistant metal (or some composite material) tubes and flex hoses that carry hydraulic fluid/pressure to actuators that make the spoilers raise up. There is a relatively less pronounced amount of electrical wiring within high integrity sheathing for sensors and various other purposes depending on aircraft type.


With the flaps set to a fully deployed landing position, and the spoilers raised, you can get a pretty good view of the flap well. The side with all the “cables and electronics” is in fact the outside of the rear wing spar. This forms one of those key components of a wing box. Fwd of that is the interior of the wing box which acts as a sealed fuel tank in the wing. Typically on the outside of that spar, you will run hydraulic lines for one of the hydraulic systems a board the aircraft which provides actuation of the primary flight controls, wing spoilers, and actuates the flap drives. You may also see wiring run along through this section as well, which provides power as well as electronic flight control inputs to the control surfaces, in the case of a fly-by-wire aircraft. It might seem a little strange but that’s a perfectly normal way to design the wings on a transport category airplane. All that stuff is waterproofed and sealed against the environment.


Are those cables and electronics?

Cables, yes. Electronics, no, other than a few sensors.

Just exposed right into the air like that?

Yes! Air is neither corrosive nor an electrical conductor under most conditions.

Isn't that bad?

Not at all. Some of the smartest minds in engineering designed these systems with one primary goal: safety.

Sure, it's on the back side, thus not immediately facing the wind, but still, what if it's snowing or raining?

Snow and rain do not affect the operation of these cables, wires, and hoses. And these cables, wires, and hoses are made of materials that are not damaged by the air nor the common contaminants in the air.

It looks downright scary to me. Or am I seeing things?

You are correct, to someone not familiar with the components or engineering techniques, it looks scary. Wait until you see how many switches are in the cockpit! I hope that this view into the scary world of aviation is your doorway into the fascinating world of aviation. Keep looking at those planes, and keep asking questions!


Remember those lines are not exposed to the airstream; they are placed in an area that sees little moisture and pressure when the plane is moving. In flight, the flaps will have moved forward, closer to them, and the airbrakes would be lowered shut, so there are not many places for air to flow inside that pocket. One bad (it would require to be flying with the airbrakes open) analogy would be driving a convertible car with the top down in the rain: as long as it does not slow down, the people on the front seats will be dry.

Once the plane lands and is parked outside in the flightline, rain, moisture, and snow can make their way there in the same way they would in the engine bay of a car.

Incidentally, they place those hoses and lines there because they are protected from weather and airflow and are easy to reach and inspect. Understand that people do a walk over a plane before flight, so the easier you can make for them to check it the better.


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