CHILD WARNING - Small Plane Crashes in Philadelphia, Causes Explosion

[akham]

Originally Posted by Hogmann

Speaking of stalls here's a great video of a Pilatus stalling.

Interesting, thanks!

PC-12 seems to be pretty unstable at stall (spins easily) but once its nose-down things seem to sort themselves out pretty quickly - probably due to the pilot stopping the spin quickly.

The last part of the video shows how important it is to have a good pusher (ahem).

[akham]

Originally Posted by William May

Yes, nobody in the Lear community that I talked to, could venture a guess as to how they GOT into that situation. That is the big question right now. The dive and the impact were pretty much accepted as the result of a stall, but how the aircraft got into a stall condition is the problem.

I'm not an expert in the Lear (or really an expert in any area of aviation, I've passed some theory exams and done a little flying) but I'm having trouble reconciling the stall theory with what we see in the (granular, accurate) ADS-B data.

By definition, a stall is AoA > critical. In most aircraft that can happen at any throttle setting.

A (wings level) stall under power in the climb out implies heavy pitch up, the sort of thing that might happen as a result of CG being too far aft. (B747 at Bagram, etc). That should be pretty obvious in the ADS-B data, and we don't see it.

Unless there was an engine failure or (inappropriate) power reduction, I don't see how the aircraft could stall in a way that is consistent with the data we have.

Once there has been a stall, I do see how the aircraft can get into a nose-down high power situation as we see in the video.

I've heard that yaw dampers on these are a notorious issue, and note that there was some yaw off course on climb out. Any ideas on that?

[Hogmann]

Originally Posted by akham

By definition, a stall is AoA > critical. In most aircraft that can happen at any throttle setting.

And any airspeed.

[William May]

Originally Posted by akham

I'm not an expert in the Lear (or really an expert in any area of aviation, I've passed some theory exams and done a little flying) but I'm having trouble reconciling the stall theory with what we see in the (granular, accurate) ADS-B data.

By definition, a stall is AoA > critical. In most aircraft that can happen at any throttle setting.

A (wings level) stall under power in the climb out implies heavy pitch up, the sort of thing that might happen as a result of CG being too far aft. (B747 at Bagram, etc). That should be pretty obvious in the ADS-B data, and we don't see it.

Unless there was an engine failure or (inappropriate) power reduction, I don't see how the aircraft could stall in a way that is consistent with the data we have.

Once there has been a stall, I do see how the aircraft can get into a nose-down high power situation as we see in the video.

I've heard that yaw dampers on these are a notorious issue, and note that there was some yaw off course on climb out. Any ideas on that?

The Lear 55 has dual yaw-dampers. But they have clutches on them, that can easily be over-ridden by the pilot's pushing on the rudder pedals. They have 2, because they have to have at least ONE operational for flight. That is why they put 2 in. All the other autopilot servos (one each for pitch and roll) can be inop, and the aircraft can still dispatch. But the yaw servos are not only for the autopilot, but also for the yaw damper system, and it is required to have at least ONE yaw damper system operational for flight. Because of it's design, Lears will "Dutch Roll" during flight if no yaw damper is operable. This is something that CANNOT be controlled by the pilots. Pitch and Roll axes can easily be controlled by the pilots, but not a yaw oscillation.

All swept wing aircraft suffer from yaw cycle problems, some worse than others. On 737's they can dispatch the aircraft with all the yaw dampers inop, but the ride for the people in the rear of the aircraft is bad. I have ridden in the flight attendant's rear seat while deadheading, on a 737 with no yaw dampers operable (They were on MEL) and it was a constant shove from left to right, and back again. Not large, but noticeable.

[William May]

Originally Posted by akham

Wow, great post! Very interesting, thanks!

Its amazing what you can do with a diploma from CSPFS.

Well, my expertise on Lears came from working on them, and flying in them so often. I wound up as a Crew Chief at their Tucson repair center, and we each handled 3-5 aircraft, with our crews of from 4-6 guys, and 1 or 2 avionics guys. I was lucky and always had REALLY sharp crews. I could put one guy on each aircraft, and I would work one aircraft, and we got a LOT done. I would only hear from them if a problem came up that they needed help with.

If you want a demo of how good those guys were, we were all standing around the r/h engine on one that was getting ready to leave after some minor thing (radar, I think, or a TCAS problem, something that only took a couple hours to fix) and we were talking with the pilots, blah, blah, blah, and mechanics, when they are just standing around, will move things. This guy moved the aileron up and down. They were operated by a cable system and move pretty easily. So he moves it, and perks up, and he moves it some more. Then he comes over to me and tells me "Hey! I think this guy has a cable wrapped in this R/H wing!"

When you change the cables on a Lear, you have to run them in individually, down the length of the wing, and they have to run OVER the flap sector, UNDER the spoiler installation, etc, etc. IT IS TYPICAL YOU WILL GET A CABLE WRAP SOMEWHERE IN THE CABLE RUN, NEARLY EVERY TIME. It was standard practice to run the new cables in, and then put some tension on them, and find and remove any of these cable wraps, where one has wrapped itself around the other cable. It is IMPORTANT TO NOTE THAT EVEN WITH A CABLE WRAP, THE FLIGHT CONTROL SYSTEM WILL OPERATE NORMALLY IN EVERY RESPECT! THIS is what made everyone so cautious during cable changes. And the question would arise at every crew change or shift change "Did you guys check for cable wraps yet?" and the answer would determine what the first thing on the list was for the next crew to do.

Well, this guy was VERY SHARP, and I trusted him completely. I called the Supervisor over, and told him, and then we talked to the customer. He had had his cables changed somewhere else, and had no problems with them, so he was skeptical. We finally told him we would drop a few access panels, take a look, and if we found nothing, we would put the panels back up with brand new painted screws, and he would NOT be charged for anything regarding it. So the customer said, "Well, go ahead and take a look" and he hung by the wing to see what the results were. We pulled probably 5 of the 8 largest panels on the bottom of the wing, and my guy got his inspection mirror and flashlight, and within about 30 seconds, said "Here it IS!" and sure enough, the cables were wrapped around each other at that point. It was in a good visibility spot as well, so the customer could easily see what we were seeing. He was definitely shaken up by that, and told us to go ahead and straighten it out. We pinned the center cable sector, disconnected just one of the cables, fished it out to unwrap it, the inspection department examined it with 10 power magnifying glasses to check for cable damage (none found, the change had been done only a few hours before and the cables had not had time to wear while rubbing) the cable was run back in, checked for routing, reconnected, and tensioned back up, and the rigging checked and adjusted. He was ready to leave the following morning, and he thanked the guy that found the wrap as well, and then off they went.

So that was how I was so lucky at my career as an airplane mechanic.

The Colombian School of Forensic Science and Plumbing was just some side schooling, (largely done on this DR website) that enabled me to learn the difference between a bullet in the forehead, and being hit by a train.

But in all seriousness, I have learned a LOT about death here. Especially posts like the ones from "Herman the Shocker", "Vedderman", and "Crux of Bag" showing such things as effects of bullet wounds, shootings at close range vs far away, and even deaths that appeared to be one thing, but were actually SOMETHING ELSE! I personally think any police officer or detective should be member of this site, to better understand what you see at a crime scene, and WHAT YOU REALLY NEED TO SEE at a crime scene. And the variation in changes from one situation to another. This site is not only very interesting, it is pretty crucial for people in the death response area, such as police and coroners, to look at the posts on here, and get a REAL perspective, that is probably far greater than what they would see in a classroom setting with 20 year old, 4-picture sets, of crimes that have been taught for years at police and coroner seminars.

I give DR 10 corns for this!

[akham]

NTSB have released their preliminary report. It tells us little that we didn't already know, except:

"The airplane was equipped with a cockpit voice recorder (CVR). The CVR was recovered from the initial impact crater under 8 ft of soil and debris and was sent to the NTSB Vehicle Recorders Laboratory, Washington, DC, for processing and readout. The recorder displayed
significant impact-related damage as well as liquid ingress. After extensive repair and cleaning, the 30-minute-long tape-based recording medium was auditioned to determine its contents. The CVR did not record the accident flight and during the audition it was determined that the CVR had likely not been recording audio for several years."

Copy of the report is attached.