AW609 tiltrotor prototype crashes during test flight

[aerolearner]

According to preliminary news reports, an AW609 tiltrotor prototype crashed during a test flight. The accident occurred at around 10am (local time) in field between Santhià and Tronzano (Piedmont region, NW Italy). The aircraft had taken off from the AW facility in Vergiate.
According to the news, both pilots sadly lost their lives.

https://www.lastampa.it/2015/10/30/edizioni/vercelli/elicottero-esplode-in-volo-tra-santhi-e-tronzano-k0Fy2opruqz9CxCMdv1aQK/pagina.html

[ShyTorque]

Tragic! :sad: What more can be said?

[SASless]

Test Flying has always been an occupation that carried a lot of risk with it no matter how carefully the Test Program was structured and carried out.

Condolences to all....as having worked for Agusta in the past at that facility and knowing what a wonderful group of dedicated Aviation professionals are there, it does sadden the Heart to hear such news.

[212man]

Very, very sad. I was at the RAeS Cierva lecture on Tuesday, listening to the AW609 Programme Director talking about it, and the future, with huge enthusiasm. I also know the British TP normally based in Arlington and hope he was not in this crew.

[tottigol]

Names of Test Pilots involved in the crash were released.
One Italian and a US National, knew them both, God has them in His embrace.
Very sad day.:(

[21stCen]

Deepest sympathies to the families, friends, and colleagues of the two pilots. Pietro's dedication and long standing involvement in the program is second to none. Both will be missed...

[21stCen]

Just heard the second pilot was H.M. A great person and outstanding pilot. The program will go on and succeed, but the loss of these two today is absolutely devastating to all involved.

[Encyclo]

Spent time with Herb in Athens and Paris some years ago. What a great and humble guy.

I was hoping he would not be in the aircraft :(

[9Aplus]

Sincere condolences to all related and all involved in program.
Let's hope that this tragic loss can lead to better safety and technology....

[Hot and Hi]

Vertical reports that according to local media reports the aircraft was on fire as it crashed.

AW609 prototype crashes; both pilots killed | Vertical Magazine - The Pulse of the Helicopter Industry (http://www.verticalmag.com/news/article/33118)

Here is the Google translation of the La Stampa article referenced form the OP:

A roar followed by a crash to the ground in the fields between Santhià and Tronzano: many in this morning saw the explosion in flight of military tiltrotor experimental Agusta Westland, hybrid of airplane and helicopter started from the basis of Vergiate, in the province of Varese.

The fear that the aircraft could fall over the area of ​​Santhià (the first houses from the crash site three hundred meters away) was great, but just the readiness of the two airmen on board has avoided the bloodbath them, Pietro Venanzi, 53 , pilot Agusta Westland and Herbert Moran, a former Navy pilot Oregon native American but lives in Varese, died on the spot but by their courage and with a final maneuver capable of bringing the media into a peripheral area, avoided a massacre.

Meanwhile, the prosecutor of Vercelli has opened an investigation for manslaughter and aviatorio disaster, as well as the ANSV, the national agency for flight safety, opened an investigation and sent an own investigative team.

Witnesses tell of seeing him lean before catching fire. It was not the first test carried out over the skies of Vercelli. "It was flying low over the houses and it was on fire - told a group of students -. The pilot did well to take him up on the corn fields. If he fell in the city, it would be a massacre. "

"We have just learned that one of our prototype test fell - said this morning the CEO of Finmeccanica, Mauro Moretti, during his speech at the conference organized at Expo -. This does not have to stop in research and innovation. "

[espresso drinker]

:( Cronaca. Velivolo militare esplode in volo nelle campagne di Santhià - LaPresse (http://www.lapresse.it/foto/cronaca/velivolo-militare-esplode-in-volo-nelle-campagne-di-santhia-1.786927?pos=1)

[bockywocky]

Very sad news indeed.
The long lasting dedication to the AW609 program of Pietro made him the lead specialist in this area.
May both RIP

[riff_raff]

Meanwhile, the prosecutor of Vercelli has opened an investigation for manslaughter and aviatorio disaster.........I don't have a knowledge of Italian law but it seems a bit unusual that a criminal investigation is opened before there is even any preliminary accident findings from civil aviation authorities.

I recall a somewhat similar situation in 1994 when F1 race driver Ayrton Senna was killed in a crash during the San Marino GP. A couple members of the Williams race team were charged with negligent manslaughter and tried in absentia by Italian prosecutors. It took several years to complete the legal process.

While it's tragic that the two test pilots lost their lives, a criminal case will likely take far longer to complete than a crash investigation by civil aviation authorities. So this could end up having a big effect on the AW609 certification efforts.

[The Sultan]

Riff

That is standard practice in Italy and is the first step in the investigation.

The Sultan

[Otterotor]

Just became aware of Mr. Herb Moran being one of the test pilots onboard the AW609. I had enjoyed several beers after work with him while at PAX discussing design attributes and issues of the H-1 Upgrades rotors. He was a great test pilot and fine human being! I too was hoping he was not in that aircraft. RIP. :(

[maeroda]

@ Rif Raf

In Italy it is usual for the prosecutor to open an investigation for manslaughter and aviation disaster...the rules goes in that direction to give the investigators all the power to inspect they need.

On there other hand we are talking about Roman Law Code merged with Cristian Church for whom misconduct, fraud and negligence are embedded in the human conduct and guiltiness must be fund.

P.S.: Sorry...just posted unaware of Sultan's answer.

[The Sultan]

AgustaWestland: AW609 was performing high-speed tests on day of crash
by Oliver Johnson
Share

Manufacturer AgustaWestland has disclosed that the AW609 prototype that crashed in Northern Italy had a flight plan that included tests at high speed. AgustaWestland Photo

The AgustaWestland AW609 prototype that crashed in Northern Italy on Oct. 30, killing test pilots Herb Moran and Pietro Venanzi, was undertaking a flight plan that included tests at high speed, the manufacturer has confirmed. In announcing further details about the fatal accident, AgustaWestland said the tests on the flight plan were to demonstrate certain capabilities as agreed with the Federal Aviation Administration (FAA) — and had already been successfully performed in previous flights.

The aircraft involved in the accident was prototype number two, registration N609AG. It had been assembled in Italy and performed its first flight on Nov. 9, 2006. It had accumulated 567 flight hours since then, and was due to complete its test flying program at the end of 2016.

AgustaWestland said that the aircraft proved fully serviceable during its pre-flight tests on the morning of the crash — and added that these tests were completed shortly ahead of takeoff and were performed in full compliance with the inspection plan authorized by the relevant aviation and certification authorities. The aircraft departed from the manufacturer’s headquarters in Cascina Costa di Samarate (Varese), Italy, at 10:15 a.m. local time.


Test pilots Pietro Venanzi and Herb Moran died when the AW609 prototype crashed in Northern Italy on Oct. 30. AgustaWestland Photo

At 10:42 a.m. local time, 27 minutes after takeoff, the aircraft’s real-time telemetry signal was lost with no further contact. Its wreckage was subsequently found near Santhia (close to Vercelli), approximately 50 kilometers (31 miles) from Cascina Costa.

The manufacturer said it was supporting a full and transparent investigation into the crash, which is being led by the Italian National Agency for the Safety of Flight (ANSV), but said formulating any theory on the possible causes of the accident was “absolutely premature” while the investigation continues. As the aircraft was registered in the United States and was operating under FAA regulations, both the FAA and the National Transportation Safety Board (NTSB) are involved in the investigation. Other investigating authorities include the Prosecutor’s Office of Vercelli (Italy), the Italian Civil Aviation Authority (ENAC) and the European Aviation Safety Agency (EASA).

With regards to the AW609 program’s future, AgustaWestland said it was “fully committed to mitigating any delay this tragic accident, and the subsequent investigation, might have” on the program. The third AW609 prototype is currently being assembled in Italy and is expected to be completed by the end of the year.

Pilot details released

Venanzi had worked as an experimental test pilot with AgustaWestland for the last 15 years, and had returned to Italy following time spent in support of the AW609 program in Texas. He also played a significant role in the testing and development of the AW139.

His achievements in flight testing were recognized in 2014, when, along with fellow AW609 pilots Dan Wells and Paul Edwards, he was awarded with the Iven C. Kincheloe Award for an outstanding professional accomplishments in the conduct of flight-testing.

Prior to joining AgustaWestland, Venanzi was the Aide de Campe for the Chief of Joint Military Staff of the Italian Armed Forces, and had a six-year career at the Italian Official Test Centre in Pratica di Mare, Italy. While there, he worked on several test programs in both fixed- and rotary-wing aircraft. He was also a display pilot at many prestigious air shows including the Royal International Air Tattoo, where he won the Sir Douglas Bader Trophy for flying the overall best air display.

Moran was an experimental test pilot with over 27 years of military and commercial aviation experience, and had been dedicated to flight-testing of the commercial TilRrotor for over 10 years. He began his work on the Bell/Agusta BA609 in 2005 as part of the TiltRotor development team in both Texas and Italy.

Prior to joining Bell, and then subsequently, AgustaWestland, Moran had a storied career in the U.S. Marine Corps, rising to the rank of Lieutenant Colonel. He served in operational and instructor tours in the Bell UH-1 Iroquois and Bell AH-1 Cobra, and was presented with the Navy Commendation Medal with Combat Valor as a result of his overseas deployment in support of Desert Storm. His military service culminated with duties as Platform Coordinator for the UH-1N Test Team and then Operations Officer at the Naval Rotary Wing Aircraft Test Squadron. Moran was instrumental in the development and flight-testing of a number of military test projects and helicopter platform upgrades during his military career.

Moran flew 35 different military and commercial aircraft variants across rotary-wing, TiltRotor, jet and turboprop platforms, and maintained both FAA and European Aviation Safety Agency pilot certifications. Prior to his work on the BA and AW609, he was Bell Helicopter’s lead pilot of a five-aircraft development team of the UH-1Y Venom and AH-1Z Viper. In 2002, his accomplishments were recognized industry-wide when the Society for Experimental Test Pilots selected him as the recipient of the Iven C Kincheloe Test Pilot of the Year award.

"Our thoughts are with their families and friends," said Daniele Romiti, CEO of AgustaWestland, “Pietro and Herb were experienced pilots with long and successful test flying careers who will be remembered for their exceptional personalities, passion and skills,” he said. “Their significant contribution to the AW609 programme and other rotorcraft programmes will be remembered by their colleagues at AgustaWestland and across the industry worldwide.”
AgustaWestland: AW609 was performing high-speed tests on day of crash | Vertical Magazine - The Pulse of the Helicopter Industry (http://www.verticalmag.com/news/article/AgustaWestlandAW609wasperforminghighspeedtestsondayofcrash)

Some additional info.

The Sultan

[SansAnhedral]

Interestingly enough, the radar track of the day's incident has been removed from flightradar 24

N609AG - Aircraft info and flight history - Flightradar24 (http://www.flightradar24.com/data/airplanes/n609ag/)

http://helihub.com/wordpress/wp-content/uploads/151030-n609ag-2x.jpg

At the time, I do recall stepping though the logs, and I do not recall ever seeing a return over 140-150kt. Perhaps the test card for the day intended to complete high speed points, but I think the headline might be a bit misleading as it implies a potential causation.

[The Sultan]

Sans,

The article stated the purpose of the test not where they were on the card. It did state they had been to high speed many times. I know Ship 1 has been faster with no issues being found with the design.

Of note: Today at their base in Arlinton, Tx Agusta held a candle light memorial to remember Pietro and Herb with the previous Bell 609 team being invited.

The Sultan

[megan]

Perhaps the test card for the day intended to complete high speed pointsApparently the aircraft was scheduled to perform high-speed testing at the time of the crash.

AW609 Crashed During High-speed Testing | Business Aviation News: Aviation International News (http://www.ainonline.com/aviation-news/business-aviation/2015-11-09/aw609-crashed-during-high-speed-testing)

[Vertical Freedom]

another Aviation tragedy.....Rest in Peace
Om

yet another for the tilt-rotors.......when will they learn; rotating nacelles are not ever gonna do well, certainly not civil
Om

[Lonewolf_50]

yet another for the tilt-rotors.......when will they learn; rotating nacelles are not ever gonna do well,
The thousands of hours of V-22 operation do not agree with your uncharitable observation. This particular prototype aircraft is reported to have flown over 500 hours.

Furthermore, these two pilots were out there as part of making something new happen, just like their "forefathers" in flight testing for the past century or so. With your attitude, Igor would never have pursued his successful rotary wing designs ... but let us save the esoteric arguments for another venue, please. These two men gave our community a lot, and sadly we lost them.

[Vertical Freedom]

Lonewolf50 when I did my theory training back in the mid eighties my teacher SD quoted that we'd all be flying these by the time we got a license. Now 30 years later there is still no civil certified version (still testing) & the military, well they do what they like....If they really were so good, so superior? then we'd all be flying them by now to the top of Everest :hmm:

[megan]

The aircraft has a customer

UAE Picks AW609 for Tiltrotor Requirement (http://www.defensenews.com/story/defense/show-daily/dubai-air-show/2015/11/10/uae-tiltrotor-aw609-beats-v22/75501164/)

[SansAnhedral]

If they really were so good, so superior? then we'd all be flying them by now to the top of Everest

You can blame modern certification complexity for an entirely new aircraft type, combined with the cost of something for a market (civil) where additional speed is not typically the main driver for profitable operations.

Otherwise, we would also be witness to a plethora of supersonic commercial airliners...don't you remember those promises in the 1980s as well?

[Lonewolf_50]

If they really were so good, so superior? then we'd all be flying them by now to the top of Everest :hmm:
Also recall that since the 1960's we've been about 15 years from getting fusion reaction sources of energy ... so maybe not every prediction you ever heard is what you should compare reality and complexity to. :8:};)

[atakacs]

567h in nine year - about 5 hours per month... I have no real expertise here but is that the typical test schedule ?

[riff_raff]

yet another for the tilt-rotors.......when will they learn; rotating nacelles are not ever gonna do well, certainly not civilVertical Freedom,

What evidence do you have that this crash was caused by rotation of the nacelles?

There are news reports of witnesses on the ground stating the aircraft was on fire just prior to crashing. Based on the reported length of time the aircraft was in the air and the distance traveled, it must have spent most of the flight in airplane mode (ie. with nacelles locked in a horizontal position).

[Lonewolf_50]

567h in nine year - about 5 hours per month... I have no real expertise here but is that the typical test schedule ? Do recall that the program went from Texas to Italy somewhere in the middle of that as Bell signed over their portion to AW.

[jcozine]

Has anyone heard anything about what caused the AW609 crash back in October yet? For a program that was supposedly so close to the finish line I'm surprised not much has come out about it.

[Lonewolf_50]

This thread is a good place for your question/post.


http://www.pprune.org/rotorheads/456619-what-s-new-civil-tiltrotor.html?highlight=aw609

[pilot and apprentice]

Not a thing there, not even a post since the accident

[The Sultan]

In Italy a crash is treated as a crime. In thi case homicide. Nothing will get out until the govt releases it.

The Sultan

[riff_raff]

Some news on the AW609 accident.

https://www.flightglobal.com/news/articles/heli-expo-finmeccanica-confident-on-cause-of-aw609-422670/

[gmrwiz]

Following the accident of the AW609 occurred last October in north Italy near the Agusta plant, on Thursday May 19th the third prototype, ready to be transferred to the Agusta plant in Philadelphia after the completion of the ground tests in Cascina Costa , has been sequestrated by the magistrate.

[atakacs]

I know that Italy has a fairly ...shall we say... unusual legal system but is this "normal" procedure ?

[SansAnhedral]

They probably want to measure the tail area

[atakacs]

They probably want to measure the tail area

Are you referring to something specific here ? If so it eludes me...

[aerolearner]

Interim Report issued by the Italian AAIB (Agenzia Nazionale per la Sicurezza del Volo, ANSV).

http://www.ansv.it/cgi-bin/ita/AW609%20N609AG%20interim%20statement%20and%20safety%20recomm endations.pdf

[SansAnhedral]

They probably want to measure the tail area

Are you referring to something specific here ? If so it eludes me...

...with the new configuration of the rear fuselage and tail fin modifications

Q. E. D.

("augmented dutch roll" due to yaw instability from a modified vertical stabiliser?)

[Ian Corrigible]

To wit:

SlowFin:

http://i.imgur.com/KONK1xs.jpg

FastFin®:

http://i.imgur.com/X9xj1BS.jpg

I/C

[SansAnhedral]

I'm sure BLR (http://www.blraerospace.com/products/details/fastfin/rotary-wing/) wants no association with this incident

Puzzling to think the engineers at Agusta/Finmeccannica/Leonardo would make a modification like this (CG/weight?) knowing the lateral flapping capability on the 609 is (currently) locked out by design.

That certainly looks to be a not-insignificant areal reduction.

[atakacs]

Ok quick read but two things stand out of my quick reading:

1. Flight recorders where severely damaged and significant information was lost. Surprising.
2. They don't really know what happened but seems to be related to unusually complex aerodynamics at the edge of the flight envelope, which was being tested at the time of the crash. Again surprising given the state of CFD in this day and age.

comments obviously most welcome :)

[Rotorbee]

:confused:
Can somebody please explain me what the lateral flapping has to do with it?
It was in airplane mode at the time. Lateral flapping should not play a role here. Where am I wrong?

[The Sultan]

ATA,

The ED-112 compliant recorder (hardware) survived with no issues. The missing parameters had simply not been implemented yet. The recorders that were destroyed were flight test insturmentation. As stated in the report the TM data had the information. Loss of data was not an issue here.

The Sultan

[212man]

Can somebody please explain me what the lateral flapping has to do with it?
It was in airplane mode at the time. Lateral flapping should not play a role here. Where am I wrong?

Where did you see that mentioned? The report says 'lateral-directional oscillation'.

[Rotorbee]

Here:


Puzzling to think the engineers at Agusta/Finmeccannica/Leonardo would make a modification like this (CG/weight?) knowing the lateral flapping capability on the 609 is (currently) locked out by design.

What would it help in that case, if it wasn't locked out? In airplane mode?

[212man]

An interesting article about it here, with a sad premonition of what (may have) happened: http://history.nasa.gov/monograph17.pdf

(page 41 onwards)

[SansAnhedral]

Lateral flapping itself isn't locked out (then the rotor would not be gimballed), however I believe there is no lateral cyclic actuator to actually control flapping in the lateral axis (yaw in AP mode and roll in helo mode is accomplished by DCP). Its my understanding that there are provisions for an actuator but it has never been installed. V-22, for example, has a flapping controller and cyclic actuator setup that can mitigate lateral flapping.

Notice the map photo and the red triangles marked "LH HIT" and "RH HIT", I suspect that the yaw oscillation caused by reduced yaw stability from a resized tail created enough unmitigated lateral rotor flapping for a set of wing strikes.

[atakacs]

Your are quite correct that the flight recorder survived - I misunderstood that part (and am still surprised that they were actually not required to be fitted in the first place...).

On a bigger picture it would seem that the aerodynamics of this aircraft are simply not fully understood, which, again, surprises me given the sophistication of CFD simulations in this day and age. What is the sticking point here ?

[The Sultan]

ATA

The original fin was sized for a reason so Bell-Boeing understood the aero very well. Note: Ship one with the original tail went faster with older software.

The Sultan

[atakacs]

Well you seem to know a lot about this beast - care to elaborate (within reasons, of course).

From what I read in the interim report things don't seem so clear cut aero-wise...

[The Sultan]

ATA

Ship 1 with original fin exceeded the accident speeds and did not crash. Pretty clear cut.

The Sultan

[tartare]

How does that go fast fin actually work?
Looking at the BLR page, they say for conventional rotorcraft it improves hot and high performance, as well as max speed.
Is that because in the hover or slow flight a wider traditional fin acts as a sail counteracting tail-rotor power in port or starboard vector?
Does a larger fin cross section inhibit higher cruise speeds?

[SansAnhedral]

The BLR fastfin system includes an area alteration which reduces inflow blockage on conventional helicopter tailrotors, plus strakes along the tailboom to enhance coanda effect.

Neither of these are relevant on a tiltrotor. Presumably the tail change by AgustaWestland once they took over the program from Bell was for weight and aesthetics.

[noooby]

And remember, this is not a fast fin and it is not BLR.

Sans, just because it went faster when it was a Bell-Agusta doesn't mean that it was any better. Faster and heavier just means less people less distance. Nobody would buy a 609 if it could carry a poodle and owner to the next town.

The entire program has been gone through and when people hear AW609, they really need to remember that many of the people from Texas are still involved with the program and that the program is still headquartered in the USA (now Philadelphia).

Weight saving measures were already being looked at by Bell to increase payload and versatility before they ran out of money (again) and had to be bailed out of the program, so let's wait and see what AW does to rectify the issues that have been identified. They have committed a serious amount of money to this program over the coming few years, so they're going to sort this out.

[SansAnhedral]

Sans, just because it went faster when it was a Bell-Agusta doesn't mean that it was any better. Faster and heavier just means less people less distance. Nobody would buy a 609 if it could carry a poodle and owner to the next town.

To be fair, I never suggested either configuration was faster (better?) per-se. Only pointed out the airframe changes made by AW which appear to be a potential causal factor of these yaw events.

[tartare]

Ah... so a normal fin might add stability in yaw vector, but acts as a barrier to sucking air through the tail rotor, decreasing tail rotor power.
Sorry for the thread drift... have watched their video, but can't quite understand how it works.
With the Coanda effect - essentially the downdraft from the main rotor sticking to, and curving around the boom performs an anti-torque function - is that right?
How does a strake make that happen?
I understand the MD-500N blowing air out a slot to make it work - but a horizontal strake just disrupts laminar airflow?
Confused...

[Lonewolf_50]

Would the discussion of the BLR fin not be worthy of its own thread?

[SansAnhedral]

Probably! But its an interesting aside as the AW 609 fin mod truly does look like the BLR fin profile.

The longitudinal strake on a round-ish tailboom causes flow disturbance and boundary layer adjustment that virtualizes an airfoil shape in profile (imagine the tailboom was shaped like a wing with its nose up, quite expensive to manufacture and structurally inefficient). However, if you take a round profile and add a (simple and inexpensive) protrusion to one side near the stagnation point, you get a very similar aerodynamic effect, believe it or not. Think of it as a sort of vortex generator.

[noooby]

Have you compared the 139 and 189 fin and tailplane? 189 has big chunks out of it too. I guess they figured the 139 had too much area on it so they reduced the size for the 189.

Now, didn't the 609 originally have a rudder??? Would that help with Dutch Roll? Or perhaps introduce some anhedral, but that would make it a nasty to run the cross shaft through the wing.

[SansAnhedral]

Unlike V-22 and XV-15, the 609 has never had a rudder. Like mentioned earlier, yaw control in AP mode is exclusively accomplished with differential collective power.

Regarding the wing, the 609 currently has a bit of dihedral, as the crossshaft coupling can accommodate a few degrees of misalignment.

[FH1100 Pilot]

What is clear from reading both the accident report and that NASA history thing is that after 60+ years of development and research, the designers still really don't know everything about how a tiltrotor flies. The accident report confirms this: The computer modeling of the aircraft behavior and required pilot inputs wasn't even close in the high-speed regime. When it began to go pear-shaped, things happened FAST!

And so the challenges facing the computer guys are immense and daunting. It's not so much a matter of "Back to the drawing board!" but "What do we do if this happens again? And will simply making the fin larger do the trick for sure?" If it is true that the old fin design was just as fast and just as stable...well...that might work. But what if it doesn't?

You have to admit one thing: In airplane mode, if that thing were a normal fixed-wing you'd say to yourself, "Man, that thing has a TINY rudder!" But it's not a normal fixed-wing.

Hey, "stuff" happens in the development of any aircraft. Perhaps Agusta will go back to the (sexier!) XV-15/V-22 tail. Probably won't be as fast, but maybe won't lose control at high speed.

Either way, this accident is a sad commentary that after all these years...after all these flight hours of testing...after all these computer models...there are aspects of How A Tilt Rotor Flies that elude us. How far has this accident set the program back? I'm sure another ten...err, twenty years of development ought to do it. (I wonder if Agusta will ever tire of throwing money down that black hole?)

[tartare]

So the accident appears due to sudden onset of unanticipated pitch-yaw coupling at high speed?
From the photo of the crash site it looked like there might have been in-flight breakup - I assume due to the sudden air loads beyond design limits.

[atakacs]

What is clear from reading both the accident report and that NASA history thing is that after 60+ years of development and research, the designers still really don't know everything about how a tiltrotor flies. The accident report confirms this: The computer modeling of the aircraft behavior and required pilot inputs wasn't even close in the high-speed regime. When it began to go pear-shaped, things happened FAST!


Indeed.

and - unless I have missed something - this happened during "classic" flight mode, not transition. My uneducated guess would have been that this part of the flight envelope to be well understood and modeled.

[SansAnhedral]

from the photo of the crash site it looked like there might have been in-flight breakup - I assume due to the sudden air loads beyond design limits.

As I mentioned earlier, large yaw oscillations could laterally flap the rotor (particularly on the 609) beyond its design limits of around 10 degrees and cause a wing strike which is why we see markers for "LH HIT" and "RH HIT" in the map, I presume.

this happened during "classic" flight mode, not transition. My uneducated guess would have been that this part of the flight envelope to be well understood and modeled.

Transition is arguably not the real tricky area as it happens at lower speeds - its high speed high dynamic load flight with flapping rotors where you typically get to the fringes.

That said, it is all highly dependent on specific rotor tuning where it would be most sensitive.

[noooby]

It did indeed break up in flight. I've seen the photos of the pieces falling from the sky on fire. It isn't pretty.

[Lonewolf_50]

So the accident appears due to sudden onset of unanticipated pitch-yaw coupling at high speed? The way I read the language was yaw-roll coupling ("augmented dutch roll") but there may be more to it than that due to FBW flight control laws being involved.

[Commando Cody]

Lonewolf seems to be on to something. Haven't we seen this kind of thing occurring elsewhere as we incorporate more computerization?:

AW609 flight control laws may have contributed to fatal accident - Vertical Magazine (http://www.verticalmag.com/news/aw609-flight-control-laws-may-have-contributed-to-fatal-accident/)

https://www.flightglobal.com/news/articles/aw609-control-laws-initiated-dutch-roll-investiga-426696/

Rotor & Wing Magazine :: AW609 Probe Cites Flight Laws Mismatch (http://www.aviationtoday.com/rw/commercial/offshore/AW609-Probe-Cites-Flight-Laws-Mismatch_88096.html#.V5lkQxKTQ5E)

[Lonewolf_50]

ANSV says the tiltrotor’s aerodynamic behaviour at high speed was not accurately predicted by the manufacturer Leonardo Helicopters; during simulator tests it proved virtually impossible to replicate the accident sequence. From your second linked article. (Commando Cody)
The limitations on simulators and simulations is that you still have to find out what the aircraft actually does when you are establishing the performance envelope that your customers can use.

(For an example I am familiar with (my brother in law's dad worked for Beach ages ago) go back 40 years and check out what happened to a T-34C as they were working their test program up toward the 300 knot spec. The tail failed in flight. When the Navy finally put it into service, the red line was 280.)

[megan]

From Aviation International News

AW609 Tiltrotor Flight Testing Resumes

AW609 tiltrotor prototype AC1 arrived at the Leonardo-Finmeccanica Philadelphia plant yesterday after recently resuming flight testing in Arlington, Texas. The AW609 flight-test program had been voluntarily halted following the fatal October 2015 crash of AC2 in Italy.

Plans call for AC1 to be be based out of Philadelphia, before being shipped to Italy for updates and modifications. The AW609, slated to be certified by the FAA, will be built in Philadelphia.

In May, Italian prosecutors impounded AC3 before it could make its first flight as part of their manslaughter probe into the AC2 crash. That aircraft was released by prosecutors last month and is expected to be shipped to the U.S. to join the flight-test program in Philadelphia, where AC4 is currently being assembled and readied for first flight in 2017.

Despite the 10-month delay in the flight-test program, as well as calls for wind tunnel retesting and redesign of the fly-by-wire flight control system by Italian ANSV aviation investigators, the company insists that the AW609 remains on track for certification in 2018.

[megan]

Accident report

http://www.ansv.it/cgi-bin/ita/Final%20Report%20N609AG.pdf

[jimcarler]

Very tragic, but test pilots know the risks

Is there any news on how the AW609 is faring in more recent tests?

[JammedStab]

The fatal crash of the second Leonardo Helicopters (formerly AgustaWestland) civil tiltrotor prototype (AC2), N609AG, on Oct. 30, 2015 at Tronzano Vercellese, Italy, is ascribable basically to the “combination of three factors”: the development of latero-directional oscillations; the inability of the fly-by-wire flight control system (FCS) control laws to maintain controlled flight; and the failure of the engineering flight simulator (SIMRX) to “foresee the event in any way,” according to the final report from Italy's National Agency for Flight Safety (ANSV—Agenzia Nazionale per la Sicurrezza del Volo). The accident aircraft had accumulated 567 hours since first flying in 2006. It took off from the company's production facility at Cascina Costa and crashed at 10:42 a.m. local time while executing a third planned high-speed descent as part of test flight T664. During the descent the aircraft entered uncontrolled flight in a series of lateral-directional oscillations, broke up and caught fire in flight before striking the ground, killing both test pilots.
Difficulty of Recovery
The ANSV said that a combination of ground debris mapping and telemetry data led it to “hypothesize with reasonable certainty” that the aircraft broke up in flight as a result of multiple prop-rotor strikes from excessive blade flapping on the wings as a consequence of excessive yaw angles reached during the fatal dive. This damaged the hydraulic and fuel lines that are positioned along the wing leading edges, precipitating the in-flight fire. The aircraft was equipped with flapping stops, but they were not designed to “contain the effects of the extreme aerodynamic forces generated during the event.” Because of the aerodynamic characteristics of the aircraft and the specific conditions created by the dive, the flying pilot's attempt to counteract the oscillations with a roll-tracking maneuver to level the wings was ineffective, partly because the FCS was designed to “couple” on more axes than the command inputs given on the single axis by the pilot.
Specifically, “Total lateral control resulting from the summation of pilot input and automatic FCS input has an effect on the yaw axis through aerodynamic coupling and feedforward and feedback turn coordination automatically provided by the FCS. Consequently, giving a command in counterphase on the roll axis to dampen the relative oscillations creates an effect on the yaw axis that can be in phase with the yaw oscillations. This occurred during the accident: the correction of the roll oscillation induced, by the control laws of the FCS, a manuever in phase with the oscillations of the yaw axis, generating a divergence of the oscillations.” The ANSV said that the “low frequency and low amplitude nature of the oscillations” made them difficult for the pilots or ground crew to perceive until the roll and yaw “reached excessive levels only a few seconds before loss of control.”
The pilot flying also made rudder-pedal inputs. As explained above, the inputs exacerbated the situation, taking sideslip to maximum values. The tiltrotor entered a dive at the 293-knot design dive speed. AC2 was fitted with a new tapered rear fuselage and redesigned vertical fin with less surface area. During the dive, the aircraft reached 306 knots.
Investigators attempted to recreate the accident flight in the AW609 SIMRX in Philadelphia using the same software and flight conditions, but could not; they came close by inserting algorithms that changed the aerodynamic configuration of the aircraft, but even then the lateral-directional oscillations developed were in a different phase. They did, however, use the exercise to verify the “great difficulty” of recovery to controlled flight under the conditions. The ANSV found the inability to replicate the accident flight in the simulator unremarkable, given “the lack of experimental data obtained previously in the wind tunnel and in-flight evaluations with those speed conditions and relating to the recent modified geometry of the tail fin; this last change was considered conservatively by entering a reduction in the tail fin area into the database and then implementing the computational fluid dynamics.”
The ANSV made several safety recommendations after the accident: more high-speed and complex-flight-condition modeling, verification and wind tunnel testing as part of the AW609 certification process; and verification of the flight control laws in extreme flight conditions, in particular reviewing their effectiveness with regard to pilot inputs and uncommanded coupling effects.
AW609 flight-testing resumed in August last year. AC3 is flying from the company's Philadelphia facility and recently completed testing for flight into known icing. AC4 is under assembly in Philadelphia and is expected to fly next year. AC1 is in Italy undergoing modifications before return to the flight-test program. Leonardo Helicopters expects FAA certification next year.