Air Force: Tiny imperfection on F-15's nose caused October crash

Air Force investigators were able to recover the front section of the Eagle’s radome, which showed an imperfection on the tip, called the nose cap. There was a gap between the radome body and the cap, with about 3/16th of an inch of sealant extruding from the section creating “an uneven aerodynamic surface,” an Air…

Air Force investigators were able to recover the front section of the Eagle’s radome, which showed an imperfection on the tip, called the nose cap. There was a gap between the radome body and the cap, with about 3/16th of an inch of sealant extruding from the section creating “an uneven aerodynamic surface,” an Air Force Accident Investigation Board report stated.

The F-15 System Program Office told investigators that an imperfection like this is consistent with wind tunnel tests that found it would cause a high enough yaw rate to create an aircraft spin.

via Air Force: Tiny imperfection on F-15’s nose caused October crash.

Attention to detail. Someone at some time likely replaced the sealant at the nose cap and did a poor job, or the sealant deteriorated over time and began to protrude, and no one noticed it.

The services used to spend a lot of time in basic training on things like making a bed with hospital corners  and shining shoes. The items on ones wall locker had to be precisely displayed according to a very exacting set of rules. These seemingly silly fetishes were no so much because the Army or the Air Force really, really likes tightly fitted blankets on a bed, but because they taught the simple concept of attention to detail. Very small things matter.  And once you learn to pay attention to small things like shining shoes and lining the toes of your shoes up on a line in the tile under your rack, you can learn other, more important details.

That’s not to say  I’ve never screwed up details. I’m quite good at making mistakes. And I certainly never enjoyed making my bunk or shining shoes. But I at least understood the reasons behind those tasks.

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  1. Paul L. Quandt

    If removing the nose cone is a red x job (and I believe that it should be if it is not), then two people missed that poor re-install. However, if it was due to deterioration, then perhaps a pre-flight check should be added to the checklist.

    Is there anyway to find out which it was at this time?

    Overall, I agree with your point.

    Paul

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  2. Shaun Evertson

    Good point on attention to detail. I’d suggest, however, that causality in this mishap is not limited to a bit of sealant. Flat spin bad, avoiding flat spin good. Avoiding the flat spin takes training and EXPERIENCE. Experience comes from flying more than 10-12 hours per month.

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  3. Quartermaster

    I’d certainly look at the part of the Radome I could see, but it would require a scaffold to check the entire mating ring.

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  4. SFC Dunlap (Ret.) 173d RVN

    “For want of a nail…”

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  5. LT Rusty

    Sorry, but I have GOT to raise the bullshit flag on this. I simply can’t believe that a 3/16″ protrusion could possibly be enough to cause the plane to become unstable. I mean, at worst, that shouldn’t be enough to require even a single click on a trim tab.

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  6. xbradtc

    Sure. It’s never just one thing in an accident.

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  7. timactual

    My thoughts, too. If true any damage, no matter how minor, would mean the loss of an aircraft. Perhaps in a wind tunnel without any means of correcting the imbalance and it was allowed to progress unchecked, but not in the real world. If true, it would mean any battle damage, no matter how minor, would mean the loss of the aircraft.

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  8. xbradtc

    Even relatively minor changes in airflow can have significant impact at the margins of the performance envelope, which is where the aircraft was when it departed controlled flight.

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  9. Paul L. Quandt

    QM:

    I didn’t mean the pre-flight by the aircrew, but the one by the maintainers who should have the necessary equipment.

    Paul

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  10. jon spencer

    That sealant story is one of those “just don’t sound right” ones.
    Now, here is a F-15 with more than a little sealant missing.

    How an Israeli F-15 Eagle managed to land with one wing

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  11. ChrisP

    I was gonna bring up the ‘missing wing’, but jon beat me to it.
    There’s more to the story than a sealant extrusion…

    Liked by 1 person

  12. LT Rusty

    Brad, I’m an engineer for chrissake. I know how relatively minor changes can have major effects, but something about this one just really stinks. They’re inspecting the wreckage from a crash site, and they’re able to point to a single line of glue as having caused a sufficient aerodynamic disturbance to cause a crash?

    I don’t buy it.

    Might have to see if I can find a decently accurate model of an F-15 and add a .1875″ smear of glue at the nose, run it through some fluid dynamics simulations. Could be interesting to see what happens.

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  13. timactual

    I would like to know a little more about the pilot and his/her experience before I blame this on 3/16″ of excess sealant. Even someone as ignorant as I am about piloting knows that if you yank back on the stick you may stall the aircraft and go into a spin. I doubt this is the first time it has happened. or the last.

    According to the report, the aircraft’s speed was less than 200 mph and was descending with a nose down attitude and the pilot had cut back power when he yanked the stick back.

    At that speed (<200mph) a small aerodynamic imperfection is irrelevant. The pilot stalled the aircraft. Period. Cynic that I am, I think they are trying to pass the blame onto some poor EM who MAY ( I don't know the specs) have screwed up a minor repair.

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  14. comanchepilot

    But then, wouldn’t slowing down expand the flight control envelope and allow the recovery?

    I’m with Timactual here – if the guy was flying along yanking and banking and then all of a sudden 90 minutes into his evolution he gets all squirrely the result of a sealant imperfection . . . . .hmmm.

    This kind of reads a lot like lets not find pilot error – any excuse will do.

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  15. comanchepilot

    I’m not thinking that 200 knots on descent with an unloaded wing is anywhere close to the edge of the performance envelope . ..

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  16. xbradtc

    Extreme AoA suggests the wing was loaded.

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  17. ChrisP

    Sure looks like “spiking the AOA” at 150ktcas stalled the aircraft.
    Yes, the pilot screwed the pooch, dumbass…

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