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A320 flew into a hailstorm 20mins from landing.

An A320 flew into a hailstorm 20mins from landing. I’m intrigued by the damage distribution. Seems like everywhere else wasn't touched at all. Why?

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    $\begingroup$ I'd love to see the engines of that plane 😶 $\endgroup$
    – Jpe61
    Commented Jun 10 at 17:35
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    $\begingroup$ @Jpe61 Jet engines eat hail for lunch. $\endgroup$
    – reirab
    Commented Jun 10 at 22:54
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    $\begingroup$ @reirab more like it is a requirement that they eat hail for lunch, and are specifically tested against them to make sure they do not fail. Engines that don't pass are not certified and cannot be used. $\endgroup$
    – Nelson
    Commented Jun 11 at 10:25
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    $\begingroup$ @Nelson Yep, that link is to the CFRs that specify the testing requirements for exactly that. :) $\endgroup$
    – reirab
    Commented Jun 11 at 14:04
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    $\begingroup$ Props to that windshield tho $\endgroup$
    – Alan B
    Commented Jun 11 at 15:18

3 Answers 3

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Although the exterior of a jet airliner may just look like uniform aluminum with windows, the construction is actually much different than the outward appearance suggests.

The front of modern jet airliners are what's called a radome, which is a portmanteau of "radar" and "dome". The radome houses a radar antenna, and the material covering the radome is much more fragile than the rest of exterior surface of the aircraft. This is to improve the performance of the antenna. Behind the radome is a structural wall that limits any impact to the radome's exterior from affecting the body of the aircraft.

This is why you see the exterior of the radome in such bad condition, but the rest of the aircraft's exterior in relatively such good condition.

Regarding the windshields, the forward windshield will almost always be exposed to the majority of weather-related impacts. This is because the aircraft is flying in a forward direction (hopefully!), thus causing the greatest forces on those windows. A simple way to think about this is to think about an automobile. The front windshield of an automobile will be most affected by driving through hail, as opposed to any side windows. When a vehicle (or aircraft) is not moving, however, impacts (and damage) will largely be determined by the installed angles of the windows.

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    $\begingroup$ "to improve the performance of the antenna" is the understatement of the year. The radar wouldn't work at all if it was covered by metal (such as the aluminium skin used on the rest of the airframe), since metals are opaque to RF radiation. That's why the radome simply has to be plastic (fibreglass). $\endgroup$
    – TooTea
    Commented Jun 10 at 10:59
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    $\begingroup$ @user721108 best theory for biased damage is that the hail was falling at an agle due to winds higher up. So the plane was most likely flying straight, but the hail carried extra sideways velocity. $\endgroup$
    – Jpe61
    Commented Jun 10 at 17:34
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    $\begingroup$ @TooTea But it is possible to make a fiberglass construction that would survive the hailstorm.. it would just be thick, and thus attenuate signals. $\endgroup$
    – jpa
    Commented Jun 10 at 17:48
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    $\begingroup$ It would appear to me that once the radome had disintegrated, there would be violent radial airflow that would tend to carry a substantial proportion of the impactors away from the fuselage. That also applies to e.g. the leading edge of the wings: they have a strongly divergent radial airflow at all times. $\endgroup$ Commented Jun 11 at 15:02
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    $\begingroup$ @jpe61 So the hail was moving with the air, but the plane was side-slipping? $\endgroup$
    – DJohnM
    Commented Jun 11 at 19:08
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The windscreen.

As you can see from the photo, hailstones struck the forward windows almost perpendicularly, and the side windows almost parallel. The window material is layers of glass and plastic, and glass is hard and brittle, so impacts up to a certain force threshold will show no damage at all, then above that will cause cracking and cratering.

That's why the forward windows are beaten opaque while the side windows aren't even scratched. This is not surprising.

The port windscreen (right side in the photo) looks to be seconds from collapse. Even a small amount of glass striking the pilot in the face at 300Kts would be a serious distraction. I can only wonder how close this flight was to total loss.

The radome.

I don't know why the fiberglass radome took such damage while the surrounding aluminum seems totally unscathed. The visible damage seems to change suddenly at the boundary while AOA does not. Perhaps there are lots of little dents that don't show in the photo.

I am guessing that aluminum, being elastic and tough, dents upon impact and then springs back into shape. Fiberglass -- glass fibers embedded in resin -- being stiff and brittle, cracks upon similar impact. So aluminum recovers between multiple strikes (until metal fatigue sets in) while fiberglass accumulates damage.

Obviously the center of the radome, perpendicular to the hailstone attack, accumulated so much damage that it collapsed inward, allowing the pressure inside the antenna compartment to instantly rise to a titanic level and pop the radome like a party balloon. That's why most of the radome is missing instead of hanging there in shreds.

Then the hailstorm quickly battered the antenna itself into useless junk, concealing all its brother hailstorms from further detection by this particular aircraft.

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    $\begingroup$ LOL, "concealing all its brother hailstorms from further detection" $\endgroup$ Commented Jun 10 at 18:58
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    $\begingroup$ I strongly doubt the windows were close to collapsing inwards. It's much easier to prevent them from falling apart than building them in a way so they stay transparent on impacts. $\endgroup$
    – Nobody
    Commented Jun 10 at 20:35
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    $\begingroup$ I second the implications that the elasticity of the aluminum helped limit damage to it. Also, the point about the windows kind of applies to the rest of the skin of the aircraft as well, most of the impacts on the wings and fuselage would have been at comparatively shallow angles as well, so the amount of damage they could cause is more limited than any impacts on the radome. I would expect the leading edges of the wings to be a bit more beat-up than the rest of the plane for the same reason. $\endgroup$ Commented Jun 10 at 20:36
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    $\begingroup$ Airplane windscreens are multilayer constructions. The outermost layer is certainly heavily damaged, but the inner layers are still up to the task of keeping the wind out and the pressure in. $\endgroup$
    – Mark
    Commented Jun 10 at 23:32
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    $\begingroup$ "allowing the pressure inside the antenna compartment to instantly rise to a titanic level and pop the radome like a party balloon", can you explain why this would be the case? The radome is unpressurized, so I don't see what should cause a big pressure difference. Also, there are plenty of cases where the radome just gets dented (without popping like a party balloon) $\endgroup$
    – ROIMaison
    Commented Jun 11 at 8:00
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Just to add something to the other answers:

What it might have happened to the radome is that it has been damaged enough to loose its structural integrity and the missing piece(s) has just flown away.

Regarding the other parts of the aircraft, it is indeed very likely that also the fairing of the wing-fuselage attachment and the engine cowlings got damaged like on this B777 but unfortunately without better/other pictures of the incident it's impossible to confirm that:

enter image description here

Note in this picture how the leading edge of the inlet has been also damaged: the leading edge of the wing and the rest of the nose might have suffered the same fate as well.

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    $\begingroup$ And look at how the angle changes to the right and left of the radome. The hail would slip off at this point, and not go smashing in at 90º. Other answers have kind of said this, but I think that's the primary difference at this particular part of the aircraft. $\endgroup$
    – Raydot
    Commented Jun 11 at 17:00
  • $\begingroup$ Good find with those photos. Does the source indicate if there is any structural damage there, or primarily cosmetic (and, of course, reduced performance)? $\endgroup$ Commented Jun 14 at 0:54

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