Bell 525 fatal accident July 2016
 

Sounds like there was an incident today with a helicopter crash in the area where Bell performs 525 flight testing

Went down
 

Fatalities. There is live stream on wfaa

Bell 525 Accident
 

Fatalities have been confirmed in a helicopter crash in Ellis County.

DPS and the Ellis County Sheriff's Office are on the scene of the crash near FM 876 and Bell Branch Road.

Bell Helicopter confirmed fatalities after its aircraft crashed. A source tells News 8 three helicopters were flying in formation when the incident happened.

Bell said in a statement the helicopter was "conducting developmental flight test operations on the Bell 525 at our Xworx facility in Arlington, Texas, that resulted in a helicopter accident."

Two farmers who witnessed the crash told News 8 they saw the helicopter flying from the northeast when it hit a power line and exploded.

One person was taken to a local hospital via EMS.

Stephanie Parker with the Ellis County Office of Emergency Management said on Twitter the FAA is closing the airspace above the crash location.

Check back for more on this developing story.

Copyright 2016 WFAA

damn.... RIP, brothers.... :(

TV report
 

Bell Helicopter aircraft on test flight crashes in Ellis County | KXAN.com

Has fairly clear video of the crash site and the tail section that appears to be separate from the rest of the crash site. My condolences to everyone involved.

Rest in Peace Brothers (another sad, sad loss for our industry)

Not sure if this figured into it, but a friend at work has a son living up in Denton area. Says that today therewas, due to a thermal inversion, a weather alert for "non-thunderstorm related wind shear." Unable at the moment to figure out how wide an area around Dallas/Fort Worth that weather pattern spread.

Crash of a 525
 

Vertical Mag is reporting the crash of a 525 during flight testing.

Condolences to the families of the 2 crew.

Very sad news.

Sad news here: https://www.flightglobal.com/news/ar...g-crew-427063/.

very sad indeed

Two killed as Bell 525 crashes during flight tests - Vertical

Horrible, RIP to those who test fly to bring us new technology aircraft.

Sounds insensitive, but I hope its not an aircraft problem. Our beleaguered industry does not need another airworthiness accident, especially with a new type which promises so much and will be a real jump in technology.

Very sad. Perhaps interesting in links above that local farmers reported a power line strike, but local law enforcement countered that.

The final flight. Ship was out at 190+ Knots.

https://www.flightradar24.com/data/a...n525ta#a406614

The Sultan

My condolences to friends and family of the lost crew members. :{

525 Relentless Prototype Crashes in Texas

According to this, the tail boom was found 457.2 meters southeast of the main wreckage. Certainly don't wanna jump to conclusions, but mid-flight separation anyone?

How accurate is that speed info of flightradar24 ?

Is that some calculated "post processed" mess by flightradar24 or is it the actual a/c speed at a historic point in time verbatim as transmitted by ADSB-out?

Perhaps we should mourn the loss of the crew and refrain from speculation as to cause for the moment.
To all my friends at Bell.Sorry for your loss. Thoughts and prayers for the crew, their families and co-workers.

Sad loss
 

RIP to our brothers. My thoughts goes to their families.

I would guess there was enough data transfer , black boxes and cvr as well as dash cam that it will be a big help on the investigation .
sad day though.

Extract from one report, "It proceeded to the south, where it flew a pattern at altitudes between 2,000 and 3,000 feet. The last data point is at 1,975 feet at a speed of 199 knots at 11:47 a.m. A witness on the ground reported hearing a loud twin boom sound before seeing the helicopter make an immediate descent. Most of the helicopter debris is highly compact, though some is hundreds of feet away from the primary crash site. Dallas television station KXAS reports a section of the tail boom was located 1,500 feet southeast of the primary crash site."

No need to wait for the CVR and FDR data:
A Bell spokesperson said there was one "chase" helicopter present as well, which is standard in test flight scenarios.

Quote:

---

A witness on the ground reported hearing a loud twin boom sound before seeing the helicopter make an immediate descent

---

Correlating that to what actually happened might be tricky given the broad range of audio interpretation on what a "boom sound" is. Megan, what is the source of that report?

Lonewolf_50

Bell 525 Flight Test Vehicle Crashes; Two Crewmembers Dead | Business Aviation News: Aviation International News

This morning the PR people at Bell announced they were suspending all promotion of the Bell 525 at Farnborough as a matter of 'respect'.

It was also announced that the CEO Mitch Snyder was no longer travelling to the UK for Farnborough for the same reason. Of course there were a number of other important Bell Helicopter programmes that he was there to promote besides the 525.

While perfectly understandable in the circumstances this is the second European media/PR event that Snyder has cancelled within a month. For the future health of the company there must surely be a limit to the number of times the CEO of any company can allow unfortunate circumstances to diminish his marketing role.

Considering the importance of the 525 to Bell and how much they have invested in it, his time is probably better spent overseeing their investigation into the accident and protecting the order book by reassuring customers.

Retreating blade stall. ??

What leads you to that guess, Sp 206?

It is much to early to conclude anything.
That said, 200kts, a new helicopter type being in initial flight envelope testing and alleged windy/turbulent conditions plus a chopped of tail could lead one to think in that direction.

Is that how a Rotor system would react to RBS.....Rotor system dipping to the rear or would the aircraft nose up and roll? How extreme would it be before the Pilot lowered the Collective and moved the Cyclic Aft upon realizing the aircraft had entered RBS?

Would there be any warning signs of the onset of RBS....what would they be?

I wondered about the airspeed too. From the FAA website FAQ on ADS-B
So that would ground speed, not an airspeed?

Would a 5-blade head be susceptible to RBS anyway?? Always 2 blades on retreating side to share the load.

When you look at RBS analytically it is generally with respect to the airspeed over the rotor disc. As you go faster eventually the whole retreating side has negative airspeed. RBS comes before that point as the blades need a higher AOA to preserve symmetry of lift. Extra blades are no guarantee against RBS.

Seems much too early to speculate. I am sure the data will tell its tale. My heart goes out to Bell, my former competitors yet we are brothers all.

Rotor Stall Behavior and Loads
 

SAS, the modern multi-bladed rotors that I have experience with at Sikorsky do not exhibit the severe roll left tendency that I and perhaps others of the S-55/H-19 generation were schooled in.

I can only speak to the S-65,S-70, S-76 and S-92 series. If you drive these rotors into stall, the N/rev vibrations go up dramatically accompanied by non-linear ( with load factor ) increases in both the rotating ( push rods e.g. ) and stationary ( MR servo e.g. ) vibratory loads. A flight test team exploring stall limitations will of course be utilizing telemetry ( TM ) and the relevant loads will be a priority data stream for real time monitoring. Typically, the test team will work to a do-not-exceed limit ( DNE ) for these loads. The DNE is established based upon accelerated fatigue load testing of said components in the test lab, and are based on a very short component life, based in turn usually on a three sigma reduction from the component failure data. It is common for test teams to cycle count fatigue damage on these parts and they are replaced, discarded as required.

As you can see, this approach and taking into account that the published report is that the subject 525 was using TM, and against the personal experience just covered, makes it seem unlikely the cause was as simple as an entry into a rotor stall condition. But I hasten to add that I don't know anything about the 525 rotor, thus I'm out on a limb even going that far. It would be fair to add that during the 39 years at SA, there were a few rotor stability issues that cropped up, each with a different cause and a different solution, and I'd guess that other OEM's are no stranger to those occurrences.

Henra had it right: let the pro's at Bell who know their rotor and new machine do what they alone are equipped to do.

Brother Dixson as usual makes a very difficult explanation sound childishly simple!

The only helicopter I know for sure I had RBS happen was in a CH-47A due to a slightly over gross external load......and it occurred in the 46-48 knot range. Being Tandem Rotor....it was a very unusual result.

We had managed to trundle off with just over 16,000 pounds of 105 MM Howitzer Ammo due to a great amount of indiscretion. We realized our mistake when the FE counted the Projectiles.....and we tweaked to the fact we had grabbed a CH-54 Sky Crane Sling Load by mistake.

SAS, just out of flight school, having wangled an assignment to the Test Board at Ft Rucker, I got to be instructed in the CH-47 by Boeing Test Pilot Jim Campbell*. Asking him re stall ( I had had two very realistic H-19 events post flight school ) in the Chinook, Jim said he had flown some of that work, and due to the lift split between the fwd and aft rotor, the aft operating with higher thrust, thus higher angle of attack, the aft rotor would stall first. He said it was therefore a sort of self-correcting situation: the aft rotor would stall first, the ship would go nose up, decelerating the aircraft and installing the rear rotor. That sound right?
* Heard later that unfortunately, Jim left Boeing for Air America and was KIA in SE Asia.

Your " CH-54 Pretend " flight might provoke some of the uninitiated to carp about failure to fill out a 365F Weight and Balance Form etc etc , and I thought you might comment re the very real issues of flying cargo in an active combat situation.

No sure about that explanation. Typically you would say that for the same lift a rotor with more blades can be smaller in diameter, and can turn faster. As the retreating blade stalls when the airspeed of the a/c approaches the speed of the rotor blade relative to the airframe, that point it reached at higher airspeeds in a rotor that spins faster.

I had an RBS experience in a Sea King, high and fast and we got a very rapid onset 1:1 lateral oscillation.


It is 5 blades, fully articulated.


RIP to the lads, and condolences to the families.

Viper 7
 

Viper, that sounds like pitch-lag instability, not stall.

Part 2: I looked in vain online for an old H-3 flight manual. There used to be a write-up on pitch-lag instability in the USN military manual.

Anyway, re H-3 pitch-lag: The H-3 rotor has some alpha-1 coupling in the geometry. In the H-3, as the blade lag angle increases ( which occurs with increased power ), the pitch angle decreases a bit. Hardly noticeable, but coming back into a hover on the 61, the pilot needs to nudge the collective up a bit more when he applies collective to come to the hover. Really a non-issue.

However, if a blade damper has a problem ( e.g. sticky relief valve ) then at higher speeds, and having nothing to do with stall*, the rotor can excite a pitch to lag angle instability. Pilots unfamiliar with the excitation may well call it a 1:1 or 1/rev, but in fact it is 2/3 per rev. Fix is to look at the dampers and check their timing.

* USN H-3 had a cruise guide indicator. The main rotor servo ( typically highest loads on the newer machines have highest loads on the aft longitudinal servo, but I honestly don't recall which servo on the H-3 had the highest loads ) had an LVDT ( linear,variable,differential transducer ) which measures the loads on that servo and feeds an indicator with range markings. Like the same system on the S-65 series, anything over 30% in indicative of increasing degrees of stall.

On the H-3, with a damper problem, one can see pitch-lag when the cruise guide will be barely indicating anything. It will be at higher power, thus faster speed, but its not a simple 1/rev. An easy way to evaluate the difference is that with a simple 1/rev, ( and assuming it is large enough to get one's attention )there is usually one blade out of track and quite visible from the cockpit. With pitch-lag, the main rotor feels and appears to wobble at a slightly slower frequency, and one can see that.

Rotor heads subsequent to the S-61 have a very flat alpha-1 geometry, that is, almost zero blade pitch change as the lag angle changes, and as a result have been absent this particular instability.

The flight test of a new aircraft involves a great deal of instrumentation and real-time monitoring by excellent pilots and engineers. Mysteries to field pilots, like Blade Stall, are easily measured and diagnosed as they start to occur in test aircraft, and watching these conditions develop is the craft of a modern test team. On all the test aircraft I flew, we had cockpit indications of the degree of stall, giving plenty of warning prior to any large stall event.
It is highly unlikely that the cause will be determined by a group of guys throwing darts at this forum, much more likely that a tragic set of individually obscure circumstances produce an unlikely chain of events that led to the mishap.
The craft of development helicopter flying is similar to clearing a mine field, where the object is to find the hazards before they trigger massive problems, using tools that find the problems before they become catastrophic. It takes about 1600 flight test hours to certify a helicopter type, and every one of those hours has a finite probability of catastrophe, even the mundane maintenance test flights and avionics check flights.
I know the Bell team well, they are pros, as good as anyone at this game. This has probably shaken them up because we all believe with confidence that our systems work well, and that data, careful test procedures and training will win every time. None the less, the nature of the unknown is to be unknown, and every now and then one of those mines goes off.
This accident is probably not an measure of the professionalism of the team, or of the innate airworthiness of the aircraft, it is a measure of the uncertainty of exploration, and the cost of being surprised.


A quote that helps explain it comes from racing driver Jackie Stewart, "Was I ever scared while driving? If I wasn't scared, I wasn't driving fast enough."