LX7 Mishap

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NTSB Prelim: Lancair IV

 

There Was A “Sudden Explosion And The Right Window Was Gone.”

Location: Leicester, MA Accident Number: ERA22LA187
Date & Time: April 10, 2022, 11:08 Local Registration: N7KJ
Aircraft: Lancair IV Injuries: 2 None
Flight Conducted Under: Part 91: General aviation - Personal

On April 10, 2022, about 1108 eastern daylight time, an experimental, amateur-built Lancair IVP, N7KJ, was substantially damaged when it was involved in an accident near Leicester, Massachusetts. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, about 40 minutes after departure, during a cross-country flight at 16,500 ft mean sea level, there was a “sudden explosion and the right window was gone.”

He performed an emergency descent and landed uneventfully.

Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the right front window and portions of the roof fractured and separated from the fuselage, resulting in substantial damage.

The airplane was retained for further examination; the window was not recovered.

FMI: www.ntsb.gov

 

The NTSB reported that the pilot flew 45 minutes to his home field for a landing, bypassing numerous airports on the way. Thoughts?

 

Jeff

georgerosel1's picture

Jeff and Others,

Jeff and Others,

Approx 4 years ago my window blew out at 25,000’ in eastern Colorado on a clear day. It was the door window originally built as the quick build door from the factory. After declaring an emergency and descending to around 10,000 feet and reduced airspeed(and more calm nerves!) I was now able to talk to ATC. I was originally flying toward the nearest airport but realized the airplane was flying normal and that airport had no services. I therefore diverted to a familiar airport with services and the flight was uneventful with normal landing. In hind site I wish I would have diverted back to my home base in Denver only 30 minutes behind me. 
 

Advise to my readers… If you have a factory installed quickbuild door window, get it checked and/or reinstalled ASAP. Original factory build procedures have been proven wrong and there is a much better way. Go to RDD or Brad Simmons for advice and/or rebuild.

… George 

I also had my pilot's side

I also had my pilot's side window and part of the door blow out in my IVP at FL220 in about 2007 or 2008.  As in most aviation situations, the best course of action depends on many factors.  My situation was a bit different than George's, as I was in IMC and ice and over the mountains of Idaho and it was the window in the door.  I was unable to proceed to the nearest airport (Salmon, ID) because it was below instrument minimums.  The plane was flying fairly normal excepting the cabin temp was cold and not pressurized.  I flew about another 40 miles at reduced airspeed to Chalis, ID that was VFR without trouble.  Certainly the most conservative action to take is to land as soon as safe and practical, yet I don't know the considerations or weather of the recent blow-out pilot.  If half the roof was truly gone, I would be most concerned with additional structural failure of the fuselage, as there is precious little sectional material remaining.

Is it Just me?

Is it Just me?

Or is there anyone else out there who is concerned about the catastrophic damage caused to the airframe when a window fails in the pressurised IV series.

I have posted on all forums, contacted the manufacturers over the years and on each occasion garnered little or no interest in resolving this safety issue.

For simplicity, lets separate the door window incidents from other windows. as far as I can determine the door windows fail primarily from poor latch adjustment or pre existing stress events surrounding "through bolts" or strut mountings. In any event the failure mode is exciting but contained to the door structure as the shock wave is prevented from damaging other parts of the airframe (flying debris excepted)  due to the hinge and latching system dissipating the loads.

However, the failure mode of the co pilot window can take with it the entire roof structure! this failure mode has been recorded on 2 occasions with similar damage. Of concern is the fact that much of the structure that carries loads from pitch inputs is missing risking total airframe failure if inputs are excessive.

We often like to comfort ourselves thinking this is the result of poor build quality when in fact this failure mode is designed into the pressurised IV's (and ES's I suspect).

I put it to You that the better the co pilots window is attached the greater the risk of significant airframe damage in the event of window failure.

If anyone is interested in help to gather information to mitigate is failure mode I look forward to a response.

Laurie

Laurie,

Laurie,

I'm going to remove the offending latches on my door to see if the AD of making sure the acrylic of the window has been replace with the epoxy/flox matrix around the bolt holes.

Not sure what failure mode is happening on the rt. front window. I'm assuming it is a stressed member. It is installed from the inside. Is the window fail mode happening in a break up of the window, into shards? Is the window blowing out as a whole tearing the carbon fiber fuselage which it is embedded? Looking at the geometry the bottom sill is pretty flat/straight. The top has some curve and the sides have more of a curve. I can see if the failure is in shards the top and bottom would have an easier time of tearing the carbon sheet. The sides has a curve shape giving the a structural component and tearing effect of the carbon will be offset by a shearing failure of the bond instead. Wind loads after failure will rapidly apply loads the the flailing shard. Why the bottom does not do this I don't know. Air stream over that area? Unless the carbon is failing the failure is in the bonding whereby carrying the structural loads to a smaller area of the bond joint fracturing the window? Or the window has a stress riser, a dent or  scratch or structural loads that appear in flight as well as the designed in loads of cabin pressure. I do think they use polarized light and can see stress loads in items like when viewed through a computer screen.  To thin in thickness of the pane would be very hard to fix/replace? Did they make different thicknesses of pane? Acrylic is brittle imo, Use or exposure to vapors/liquids of some chemicals can degrade the structural integrity. Only happens under pressure. They must be breaking up into shards. I don't see the perimeter carbon failing and the whole window leaves the plane as one piece, or is it? I have no idea what is happening here but sure in interesting and important.

When the windows are fitted,

When the windows are fitted, pressing them into place (as is often done, from what I understand) can cause continued stress on them.  Acrylic windscreens are shaped at somewhere around ?   280-degrees F or more?    I have a friend who heated the windows to around 220-230 to fit them in (and also vacuum-bagged them into place) but he's a bit fanatical about building.  He also mentioned that solvents contacting the acrylic can cause some shrinking, which can cause stress to structures and crazing.  Crazing of the acrylic could be a possible cause of these failures, if the windows are breaking up, rather than the surrounding structure failing.  

 

Laurie,  you are not the only

Laurie,  you are not the only one concerned with catastrophic damage upon window failure.  Not much info on the topic unfortunately.

The LX7 that had the recent mishap was serial number 07 so well before the S/N cut-off.  Although only at 16,500', the cabin pressure was apparently up around 5-psi.  No window failures reported on an LX7 at cabin pressures below 4-psi but clearly an issue that RDD is trying to address with the mandatory window replacement.