Airlines PNG Dash 8 fatal crash in PNG [Archive]

backseatjock

13th Oct 2011, 21:57

News report from Friday edition of 'The Age' newspaper gives a few more details:

An Australian pilot has survived a plane crash in Papua New Guinea's north coast in which 28 people are believed to have died.

Only four people are believed to have survived the crash in dense forest, near the mouth of the Gogol River, about 20 kilometres south of the resort centre of Madang.

Airlines PNG Dash 8 plane, which was carrying 32 people, was on a flight from Lae, PNG's second largest city, to Madang, when it crashed about 5pm (6pm AEDT) yesterday.

"All I can tell you is there have been reports of survivors and reports there have been fatalities," the PNG Accident Investigation Commission's (AIC) spokesman, Sid O'Toole, told AAP. He said it wasn't clear how many survivors there were.

The 64-year-old Australian pilot, from Queensland, has decades of experience flying in PNG. The other survivor was a New Zealand pilot, a Department of Foreign Affairs and Trade (DFAT) spokeswoman said.

She said there were no indications at this stage that Australians were among those who died, adding that the Australian High Commission in Port Moresby has been liaising with Airlines PNG and local authorities.

Consular officials would be travelling to Madang today, she added.

Airlines PNG grounds its fleet

Airlines PNG confirmed one of its Dash 8 aircraft has crashed near Madang and grounded its fleet of 12 aircraft until further notice.

A spokesman for the Australian Transport Safety Bureau (ATSB), Australia's national transport safety investigator, said they had not been contacted to assist in investigating the crash.

The ATSB has previously assisted the AIC in crash investigations.

NDVP

13th Oct 2011, 22:40

APNG PRESS RELEASE

POMSOX/MEDIA RELEASE
Port Moresby – 10.30pm, Thursday 13 October, 2011
AIRLINES PNG ANNOUNCMENT
We are sad to confirm that there has been an accident involving an Airlines PNG Dash 8
aircraft near Madang late Thursday afternoon.
Emergency services have been activated and Airlines PNG is co-operating with authorities
to mount rescue and recovery efforts.
There were 28 passengers and 4 crew members on board. There appear to be some
survivors while a number of people remain unaccounted for.
Airlines PNG is working with the emergency service authorities to confirm this information
in more detail.
A full investigation is underway by authorities and Airlines PNG as to the possible cause of
the accident.
Airlines PNG fully supports the action of local authorities at Lae who have quarantined
aviation fuel at Lae airport from where the aircraft originated.
Airlines PNG has also grounded its Dash 8 fleet of 12 aircraft until further notice.
Our prayers and thoughts are now with all those affected by this very sad day for Papua
New Guinea.
Ends/

Loose rivets

13th Oct 2011, 23:19

FF 'Headlines' More than 20 planes have crashed since 2000 in Papua New Guinea.

Experienced skipper this time. Sounds like a challenging place to fly, with a large possibility of being a long way from a road if you do come down.

VolLibre

14th Oct 2011, 02:55

From the Post-Courier

Post-Courier Online (http://www.postcourier.com.pg/20111014/frhome.htm)

There were reports of a fire on board and that both engines had failed as the plane began its descent.

Also mentioned by a Radio Australia PNG correspondent in an interview this morning

Skipskatta

14th Oct 2011, 09:37

Fire onboard and both engines out? That sounds a bit strange.

The weather in the area has been reported as being very bad? The pictures of the burnt out plane seems to suggest that the impact was severe (maybe CFIT?).

paulg

14th Oct 2011, 10:18

Skipskatta I am not sure what pictures you refer to. Do you have a link? There was a post in Planetalking which indicated that News Ltd online had erroneously posted a picture of a burnt out wreck that was in fact of another accident.
Here is the Planetalking link: News.com.au cheats on PNG crash photo | Plane Talking (http://blogs.crikey.com.au/planetalking/2011/10/14/news-cheats-on-png-crash-photo/)

tail wheel

14th Oct 2011, 23:47

There are photos on the ABC web site, linked to the thread in Dunnunda Forum.

RetiredTooEarly

19th Oct 2011, 00:08

Another rumor getting round is that the crew were doing a DME arrival in bad weather, got above VMO, had a propellor over speed, destroyed the engine (fire) and all over Red Rover! :rolleyes:

No idea how this rumor got its legs but sounds feasible ......... Maybe! :eek:

Heathrow Harry

19th Oct 2011, 10:45

you don't have many options in PNG or Irian Jaya if something goes wrong - best to aim for the sea or the river if you have a chance

RetiredTooEarly

21st Oct 2011, 05:35

Just received a bit of info from a contact in PNG who says the above rumor re prop overspeed on an out of control DME arrival has been "confirmed" by other crew(s) of the airline involved.

Still no guarantee of this being 110% correct but looking like is was the culprit!

ABINGDON

31st Oct 2011, 20:25

Local newspaper reports observers on ground saying that aircraft passed low overhead and was 'dripping fuel' which was burning in the trees.

Also that the emergency doors were open as the plane went towards the sea.

It seems that the fuel problem certainly contributed to the flash fire which happened when the aircraft grounded. One passenger escaped 'through a crack in the fuselage' with severe burns.

listria

7th Nov 2011, 17:30

Sorry, not the original source....
OVER-REVVED PROPELLERS FOUND IN PNG CRASH PROBE - Nov. 7, 2011 (http://pidp.eastwestcenter.org/pireport/2011/November/11-07-08.htm)

Melax

7th Nov 2011, 22:01

Any twoter drivers out there to explain to us how you could overev both Props 60% ?? Major pilot Error ? I really would like to know. Thanks

I.R.PIRATE

7th Nov 2011, 22:09

Why do you want to hear from Twotter pilots when it was a Dash 8??

Melax

8th Nov 2011, 01:44

OOPS:8, My Bad ! I was thinking about another crash In Papua, that one was a DHC-6.
OK Any DASH 8 Drivers ?

Gooneyone

8th Nov 2011, 23:07

Overspeed of 60% would be almost 2000rpm. Major failure as at this Np the engine would be decelerating to try to limit the Np. Never heard of an overspeed this great - and on both props? Suggest we await further reports as this sounds unlikely.

EDIT: Take off Np 1200

henra

10th Nov 2011, 20:42

Any twoter drivers out there to explain to us how you could overev both Props 60% ?? Major pilot Error ? I really would like to know. Thanks

The fact that it happened on both sides to me is an indication that the probability of a direct mechnaical failure of the propeller control as root cause might not be so terribly high.

One thing that crossed my mind:
Could it be that they accidentally entered too steep a dive and tried to use the propellers as speed brakes ?
Would be interesting to know the propeller pitch setting at the time.

Gooneyone

10th Nov 2011, 21:48

This might have absolutely no bearing on this accident, but Bombardier sent out a FOSL yesterday advising against moving the power levers below Flight Idle (i.e.into Discing) in flight. One possible - or should I say likely - result would be a prop overspeed.
Interesting timing of the FOSL.

Pilot DAR

10th Nov 2011, 22:17

I've never flown a Dash 8, but I have fair experience in DHC-6 and Caravan. On both those types, rapidly moving the propeller levers from coarse pitch to fine pitch can get you close to an overspeed, though 60% over seems very hard to imagine. The key is that power lever movement alone should not really result in significant overspeed, as the governor should govern. I speculate that overspeed risk is cause by mishandling the propeller levers.

What would happen if the propeller controls were moved toward feather in error, and then rapidly moved back to fine to correct things, while lots of power was applied? Could the governor change the blade angle quickly enough to prevent an overspeed?

Though I respect what Bombardier would instruct about the operation of the Dash 8, I would speculate that if a pilot selected power below flight idle in flight, that would initially result in a lower propeller speed, as there would not be much engine power commanded to turn the discing propellers. The discing propellers would have some of the blade in reverse pitch, thus large torque required to turn the prop.

Just me thinking, I have no knowledge of the accident....

Gooneyone

10th Nov 2011, 22:54

In discing the blade angle decreases from 17.5 to a minimum of 1.5 degrees. However, there is no significant change in Tq.

The Bombardier AOM states:
"When the POWER Levers are moved aft of the FLIGHT IDLE gate in-flight, the Propeller Governor, Propeller Overspeed Governor and the BETA Backup logic protection are all inhibited
and Propeller speed control is no longer available. In this condition the propeller(s) would be
driven uncontrollably toward a Reverse pitch condition resulting in an overspeeding propeller
and substantial engine damage leading to possible engine failure."

However, if this was the case, I suspect the plane would come straight down. I've never heard of a prop overspeed of 60% due to Condition Lever(s) being moved too rapidly and I suspect if such a thing did occur, the manufacturer would send out a crew advisory.

India Four Two

11th Nov 2011, 23:32

Preliminary report can be downloaded here:

http://www.atsb.gov.au/media/3482404/png%20aic_11_1010%20p2-mcj%20preliminary%20report_1.pdf

Melax

12th Nov 2011, 00:54

It seems that at least one prop (From one of the the preliminary report Photos) is feathered, so how can you get 60% over speed on a feathered prop ? I'm not a -8 Driver but it just puzzles me... 28 deaths, I really want to find out what happened !

henra

12th Nov 2011, 08:29

so how can you get 60% over speed on a feathered prop ?

Maybe they just fearthered after the engines failed (which did happen according to this report) due to the overspeed?

BobnSpike

12th Nov 2011, 19:15

Here is a clue:

http://www.airdisaster.com/reports/ntsb/AAR94-06.pdf

Not saying this is what happened here, but way back in '94 a Saab 340, for some reason (read the report) ended up with both engines in reverse range in flight. Both props ran away; one going to 142%, the other to 158%. Both engines flamed out, but they were able to get the engines running again.

Didn't help, though. In a free turbine engine there is no direct mechanical connection between the compressor (gas generator) section and the power section (which drives the propeller). While the overspeed event did not damage the compressor sections, it destroyed the power turbines in both engines. So even though both were successfully restarted, with the power turbine blown out the back like a mouthful of sunflower seed husks, there was no way to deliver power to the propellers.

Unlike the accident in PNG, there were no serious injuries among the pax and crew of the Saab. And again, I am not saying this is what happened. but there are similarities between the preliminary report on the PNG crash and the NTSB report referenced above.

Livesinafield

13th Nov 2011, 00:24

Possibly just feathered the prop after the overspeed causing a loss of control

twochai

13th Nov 2011, 01:16

The HS prop on any PW 100 series engine will be driven to feather after loss of oil pressure by springs after any normal, or abnormal shutdown.

Waghi Warrior

13th Nov 2011, 02:21

There is no feathering springs in the prop hubs. Piston inside with engine oil on both sides, the system is controlled by a hydraulic (engine oil) propeller control unit (PCU), oil is ported in and out of the prop via a transfer tube.

Clandestino

13th Nov 2011, 12:00

Here is a clue:

Very good clue, I'd say.

The HS prop on any PW 100 series engine will be driven to feather after loss of oil pressure by springs after any normal, or abnormal shutdown. No it won't. What You wrote is valid for PT6. PW100s are radically different.

Possibly just feathered the prop after the overspeed causing a loss of control I'm not sure that I understand... what caused the loss of control? Overspeed or feathering? What makes you think that loss of control was involved?

Melax

13th Nov 2011, 13:10

Bobnspike, The AE accident relates to a different engine type and systems. I'm not sure this is what happened here. In that case the Capt may have selected reverse beta, just like the Twin Otter crash in St Barts.
French BEA report (french) here: http://aviation-safety.net/go.php?http://www.bea.aero/docspa/2001/f-es010324/pdf/f-es010324.pdf

BEA english report: http://www.bea.aero/docspa/2001/f-es010324a/pdf/f-es010324a.pdf
ASN page : ASN Aircraft accident de Havilland Canada DHC-6 Twin Otter 300 F-OGES Saint-Barthlmy (http://aviation-safety.net/database/record.php?id=20010324-0)

punkalouver

13th Nov 2011, 13:12

If not approved, placing power levers below flight idle on a turboprop can be very dangerous. The F50 has a different propeller(Dowty) for its PW100 engine but as this accident report shows, the three second time period that it was done on this aircraft was fatal. Do a 360(or some other safe manouver) if you are too high.

http://www.skybrary.aero/bookshelf/books/677.pdf

training wheels

13th Nov 2011, 13:56

From the preliminary report, they were at 13,000 ft with 24 miles to run before Madang. This seems to be quite high. At what altitude should you be at 24 miles for a normal descent profile (assuming already clear of terrain)?

Teddy Robinson

13th Nov 2011, 14:33

FL80 or thereabouts ... depending on the platform altitude /entry point for the procedure ... and of course terrain in that sector. The above assumes terrain is not an issue.

BobnSpike

13th Nov 2011, 15:10

The CT-7's and PW-100's both have a free power turbine. Additionally, in both engines, coming over the gates into beta or reverse disables the propeller overspeed protection. The preliminary report states that according to the FDR on the Dash, the props went to 160%, which implies the overspeed protection was not operating.

Even with the Dash's good descent performance, 13000 at 24 miles is way high. I am not familiar with the terrain in PNG, but discounting terrain issues, a standard descent ratio is about 3:1, making the correct altitude at 24 NM 7200 ft.

Island-Flyer

14th Nov 2011, 03:24

If the propellers were placed into DISC (retarded below the flight idle indent) it is possible the aerodynamic forces of a rapid descent could cause the propellers to overspeed. In normal flight configuration the DHC-8 has an automatic safety feature that will drive the propeller to coarse pitch if it exceeds 1208 PRPM. This is driven by engine oil pressure pushing on either side of a piston and tachometer. In the oil is lost the propeller will lock its pitch.

Bombardier already has issued warnings about reducing the power levers below flight idle and in US air carriers a placard is mandatory stating this prohibition.

As a manager at another DHC-8 operator in the Pacific I will be interested in seeing how this investigation plays out.

Gooneyone

14th Nov 2011, 21:41

Actually Island-Flyer, the Bombardier AOM says that in flight selection below Flight Idle the "props would be driven uncontrollably to a reverse pitch condition"
This would probably overspeed the power turbine resulting in failure. If the crew in such a situation was lucky enough to get the props out of reverse, the only option left - with the power turbine failed - would be to feather the prop(s)

macdonaldjames93

14th Nov 2011, 21:44

A standard 3x profile on a Lae-Madang track will not work, bcoz of the high terrain you have to clear and Madang is just across the bay after you've cross those big rocks.
Just a quick question, does the Dash8 do overspeed test on there run ups like they do in the Otter? I've only seen Dash do Auto FX test on there run ups?

27ace

14th Nov 2011, 22:03

In response to the question on the overspeed governor on the DHC-8, the overspeed governor test is now an engineering fuction and is not carried out by the flight crews on the normal first flight of the day checks.
Slight thread drift here, but similarly the T-handles are not pulled to test the fuel shut-off valves, we only test the loops for continuity, and the fire bells and fire detect lights in our company. This has also been relegated to an engineering fuction.

BobnSpike

14th Nov 2011, 23:24

I figured terrain would be an issue.

13000 feet AGL at 24 NM is 540 ft/NM. That's pretty steep. At 180 knots groundspeed that would require just over 1600 ft/min descent rate. At 240 it would require just under 2200. Distance required to slow and configure would further steepen the required descent angle.

Perhaps someone with experience in the Dash can let us know whether those descent rates are practical.

BBN RADAR

15th Nov 2011, 13:42

First of all their track was not Nadzab-MD direct, but rather via waypoint Yati (keeps you in the large markham valley). DME arrival into Madang requires a 2x profile due to the Finistere range. 2000fpm, 220-230KIAS and flight idle makes this easy. put the props up to 1050 if required for extra drag. 13000' at 24 miles is no big problem.

As the power levers are retarded towards flight idle, the prop governor hits the low pitch stops at 26 degrees blade angle. This area between 26-19 degrees (flight idle) is now flight beta where the HMU (hydromechanical fuel control unit) and ECU (electronic control unit) are controlling engine and prop rpm directly via fuel scheduling. The powerlevers are in direct control of blade angle in beta.

As the flightcrew actually set off the overspeed warning horn and consequently pulled powerlevers back to flight idle it seems possible that aerodynamic force caused the props to overspeed (the governor being taken out of the loop) and the HMU and ECU could not reduce fuel flow because the powerlevers are already at flight idle. This is a big design fault from Bombardier and they know it, but don't want to admit it. The FAA also knows it which is why they issued their beta-lockout protection AD dating back to 2006. Under the right (or wrong) circumstances this could happen again.

Hope this is clear.

BobnSpike

15th Nov 2011, 14:14

So if I understand you correctly, aerodynamic forces can overspeed the props with the power levers in flight idle? Wow.

Thanks for clearing up the descent angle thing.

ms21043

15th Nov 2011, 16:05

BBN RADAR

16th Nov 2011, 04:47

BBN radar, I find your scenario hard to believe. First off the D8 fleet has has over 20 million hours, this would have happened a lot more times, and we would know about it. This engine/ propeller system is used on other aircraft and as far as I know, what happened here has not manifested itself as being a problem.

I agree, it is hard to believe, but apparently, this is the 11th time this has happened (but maybe the only time it's happened to both engines?). We do know about it, that's why there are multiple ADs issued worldwide to prevent it; FAA, UK CAA, and now PNG CAA and shortly Australian CASA. Transport Canada will not mandate it, because to do so would make Bombardier admit fault and this would cost them hundreds of millions of $$$$ in law suits worldwide. Bombardier supply the kits for the beta-lockout (at a nice cost of course ;) ) and if they admit a design fault, then they would probably have to supply them free of charge worldwide.

I was told of a similar case happening in a Brasilia where they lost one engine under similar circumstances and the remaining (badly damaged) engine just got them home. I'm fuzzy on details so maybe someone else knows the story?...

How many times has a crew oversped an airplane with this engine/ propeller combination, what would they do first if they're overspeeding and they have the power levers forward? I'm sure pulling back power in response to an overspeed is not unusual. If this is some kind of anomally that shows up once every 10 years, why did both props overspeed at the same time?

good questions. If I was flying Dash 8s for a different company and after reading this I wouldn't tempt fate and would make sure to raise the nose to reduce airspeed as well as reducing power. Something interesting to note is that after the left engine destroyed itself (less than 3 seconds after initial airspeed overspeed, and reaching 2000rpm) the right engine also oversped and then feathered itself. Neither P&W, Hamilton standard nor Bombardier have been able to explain why this occured.

One thing that does come to mind here is a malfunction of the gate itself. The gate is spring loaded down, if for some reason it wasn't down and the crew pulls the PL's back to flight idle and the gate isn't there... Anyway, the beta lockout system on US registered D8's is there to prevent this, it should mandatory worldwide.

Yeah, possible. Or the PF may have accidentally raised the gate release triggers. Only one of them needs to be lifted 2mm for both power levers to come back from flight idle! Since the accident, our new flight standing orders are; that airspeed must not exceed Vmo minus 30 knots, condition levers must be at 1050 rpm (up from 900 in cruise) prior to descent AND (basically) that fingers must be kept well away from gate release triggers until wheels are on the ground.

Yes, the beta-lockout should be mandatory worldwide! No arguments there!

ironbutt57

16th Nov 2011, 06:10

At least one of the EMB-120 was caused by premature wear in the propellor hub which caused the propellor blades to go below the flight idle blade angle, and into the beta range, resulting in loss of control, and loss of the aircraft, and all on board....( ASA..Senator John Tower accident)

LimaFoxTango

16th Nov 2011, 13:53

Yeah, possible. Or the PF may have accidentally raised the gate release triggers. Only one of them needs to be lifted 2mm for both power levers to come back from flight idle!
I had heard this theory before and thought it sounded very strange. So, yesterday, while on the ground with engines off, I tried it and proved that this is NOT so. For BOTH power levers to be brought aft of the flight idle gate, BOTH triggers have to be lifted. I tried it on two different aircraft and had the same result. Lifting any one trigger will not cause both levers to move. Whether or not this magically changes inflight, well I'm not brave enough to find out.

EDIT: This was done on Dash 8 300's in case anyone was wondering.

Skipskatta

16th Nov 2011, 21:38

Widerøe had an incident that sounds similar to me, back in 2006. Found a preliminary report at the Norwegian NTSB, it only contains a short summary (roughly translated with Google translate):

"Serious aircraft incident with Wideroe LN-WIE. Early during the approach to Sorkjosen the plane came into strong turbulence. The right propeller experienced uncontrolled overspeed so that the engine had to be shut down. The aircraft banked heavy to the right and lost approx. 1000 ft. The approach was aborted and the aircraft returned to Tromsø. Major damage to the right engine / propeller. Available information indicates that when the aircraft was slowed down because of turbulence, the power levers accidentally came into the area for reversing the propellers. It is considered that the power levers should be modified. In the meantime, the company has implemented measures to prevent recurrence. Immediate recommendation sent to the Canadian Aviation Authorities February 2007. It is advised that the power levers are improved and that all operators are cautioned against the danger of inadvertent reversal in the air. The case is still under investigation."

The report in Norwegian can be found here: 06/120 | sht (http://www.aibn.no/Luftfart/Rapporter/06-120)

Widerøe's internal investigation report (in Norwegian): Widerøe: Widerøes granskningskommisjon: Ingen feil på Wid... (http://www.euroinvestor.no/news/story.aspx?id=9348243)

Norwegian newspapers reported on the incident, and my summary is as follows:

The internal investigation carried out by Widerøe, says that the autopilot was turned off because of strong turbulence. The plane was at 9000 feet. The passengers disputes this, saying that before the landing there was calm, no turbulence. There was a sudden "revving" of the engine. The plane lost 300 meters, it banked 60 degrees to the right, and 17 degrees nose down (obviously this information was provided by Widerøe, who was in contact with the passengers on the results of their internal investigation). The RPMs of the propellers was so high that the sound barrier was broken, and the bang could be heard in several places in the North of Troms (the county). There was smoke in the cabin. When the plane landed there was oil spill and visible damage to the engine:

NRK.no - Troms (http://www.nrk.no/nyheter/distrikt/nrk_troms_og_finnmark/troms/5504864.html)

Scary incident, no doubt. Is this what happende with the Airlines PNG Dash 8? Only with both engines?

lomapaseo

17th Nov 2011, 02:31

The RPMs of the propellers was so high that the sound barrier was broken, and the bang could be heard in several places in the North of Troms (the county).

Did the official report really say that or is the explanation of the noise imagined by the press ?

fdr

17th Nov 2011, 06:15

If BBN's scenario holds water... (I am only conversant with the T56 in this regard which had it's very own set of weird prop issues with the HS) then there would be a bit of an issue brewing...

BUt... I am missing something in BBN's rationale; if the power levers are retarded, then the blade pitch will fine until achieving the FFPS, at which point it will result in an under speed condition that is countered by fuel scheduling, ie it becomes a minimum thrust condition. ( it is not uncommon for various TP's to have cases where a rapid power lever closure will result in a momentary increase in thrust at part of the operation). The blade at all times is free to increase pitch without any limitation, up towards feather. The FCU/Prop Gov must indeed be unusual.:confused:

§ 25.33 Propeller speed and pitch limits.

(a) The propeller speed and pitch must be limited to values that will ensure—

(1) Safe operation under normal operating conditions; and

(2) Compliance with the performance requirements of §§25.101 through 25.125.

(b) There must be a propeller speed limiting means at the governor. It must limit the maximum possible governed engine speed to a value not exceeding the maximum allowable r.p.m.

(c) The means used to limit the low pitch position of the propeller blades must be set so that the engine does not exceed 103 percent of the maximum allowable engine rpm or 99 percent of an approved maximum overspeed, whichever is greater, with—

(1) The propeller blades at the low pitch limit and governor inoperative;

(2) The airplane stationary under standard atmospheric conditions with no wind; and

(3) The engines operating at the takeoff manifold pressure limit for reciprocating engine powered airplanes or the maximum takeoff torque limit for turbopropeller engine-powered airplanes.

Skipskatta

17th Nov 2011, 07:01

Did the official report really say that or is the explanation of the noise imagined by the press ?

From reading the article, I'd say that this was a statement from a passenger: - Makkverk av Widerøe - iTromso (http://www.itromso.no/nyheter/article41185.ece)

While searching the internet for more information about this incident, I found an article saying that Widerøe had decided to make modifications to the engine controls, because one of the power levers accidentily had been placed in the reverse position. This modification would be done on Widerøe's 26 -100 og -300 models, when Bombardier could supply the necessary equipment and software: Bygger om 26 fly - Nordland - NRK Nyheter (http://www.nrk.no/nyheter/distrikt/nordland/1.465509)

fdr

17th Nov 2011, 07:43

The suggested similarities of the ASA EMB120 is questionable; (ATLANTIC SOUTHEAST AIRLINES, INC., FLIGHT 2311 UNCONTROLLED COLLISION WITH TERRAIN AN EMBRAER EMB-120, N270AS BRUNSWICK, GEORGIA
APRIL 5,199lAAR92-03 Section 1.16).

While the EMB120 had a runaway prop, it was directly related to abnormal wear conditions and associated abnormal behaviour of the prop hydraulic system. This is unlikely to be the case in a dual failure event as in the APNG event.

ms21043

17th Nov 2011, 15:23

BUt... I am missing something in BBN's rationale; if the power levers are retarded, then the blade pitch will fine until achieving the FFPS, at which point it will result in an under speed condition that is countered by fuel scheduling, ie it becomes a minimum thrust condition. ( it is not uncommon for various TP's to have cases where a rapid power lever closure will result in a momentary increase in thrust at part of the operation). The blade at all times is free to increase pitch without any limitation, up towards feather. The FCU/Prop Gov must indeed be unusual.http://64.19.142.10/images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/confused.gif

Some info on D8 prop O/S governing:

D8 O/S governing is by one unit on each engine hydraulically and pneumatically. The O/S gov will provide O/S governing in constant speed and in flight beta range. If NP exceeds 1256 rpm, the O/S gov will hydraulically increase blade angle. When NP decreases below the overspeed point, the O/S gov goes back to normal prop governing. If the prop continues to overspeed, the cycle will repeat until the cause is removed. In ground beta range, only the pneumatic section of the O/S gov is available to reduce fuel flow. Pneumatic is also backup O/S governing in flight beta and constant speed mode.

Beta backup and beta lock out protection:

In case of prop control unit malfuntion, and bladeangle goes below 16.5 degrees with PL's above the gate, the beta backup system will operate the feather solenoid on the PCU to increase blade angle. The added Beta Lockout System is not found on all D8's, but will prevent low blade angle if the PL's are inadvertently brought below the gate in flight.. Keep those PL's above the gate in flight!

O/S governing with PL's below the FI gate:

As PL's go below the FI gate, the PCU will isolate the speed governor control and terminate O/S control by the hydraulic section of the O/S gov. This leaves O/S governing to the pneumatic section of the O/S gov, there will also be no beta backup protection.

Willie Everlearn

17th Nov 2011, 16:41

With all due respect, any pilot who uses discing, beta, or reverse to increase his descent needs his head examined. When was that authorized as an approved method?
How are Transport Canada and Bombardier responsible for this crew's stupidity.
Everything I've read so far on this (unfortunate and unnecessary) accident suggests this crew used this method to descend and I can't see where any of the manuals present this method as "acceptable".

I doubt TC or Bombardier can fix stupid. So,you might want to ask yourself why there's a warning at the idle detent and why would you think there needs to be a beta lockout?

Could it be that unacceptable old-wives-tales have prevailed over responsible airmanship and getting away with stupid practices haven't yet resulted in an accident, so it's okay to use this method of increasing a descent.

Wow.

Willie :ugh:

BobnSpike

17th Nov 2011, 16:54

Nobody has stated that as the cause. We have speculated a lot, but there has also been speculation about design deficiencies and mechanical problems.

In some of the precedents cited, formal boards of inquiry have released probable cause statements in which it is determined that deliberate selection of beta mode in flight led to the accidents. Such is not the case here. All that has been released by the official investigative agency in this regard is that the propellers oversped by a considerable degree. There has been no determination by anyone (other than you) as to what caused the overspeed to occur.

lomapaseo

17th Nov 2011, 19:58

In some of the precedents cited, formal boards of inquiry have released probable cause statements in which it is determined that deliberate selection of beta mode in flight led to the accidents. Such is not the case here. All that has been released by the official investigative agency in this regard is that the propellers oversped by a considerable degree. There has been no determination by anyone (other than you) as to what caused the overspeed to occur.

All true, but then some speculators on a thread like this do need to understand the limits of the word game

Kiwiconehead

17th Nov 2011, 20:09

This was done on Dash 8 300's in case anyone was wondering.
Registered where?

UK CAA has a different FI gate requirement, separate for each PL i believe.

Rest of the world if one trigger is up they should both go thru as the gate cam/mechanism is a single piece..

I know if one PL is below FI the other will go straight thru as well - use it when I'm rigging power lever layshaft microswitches so you get smooth operation thru the gate especially setting up the beta backup switches which are at FI -2deg.

fdr

17th Nov 2011, 20:15

Thanks for the info ms21043, that appears to be a fairly normal Turbo-propeller controlling process. The normal operation naturally relies in being in flight mode, and in such mode the protections are conventional.

For this event, either two independent systems (LH PCU, RH PCU) suffered relatively uncommon failures in a very short period of time that inhibited the normal protections of the propellers, or some other cause occurred. The only common items to the propellers is effectively the:

operating envelope
environmental conditions
crew PL inputs (potentially)

The report will be interesting reading. For other operators of the Dash, you do need to be careful about movement of the PL's towards Beta inflight. Accidentally entering beta at high IAS and/or TAS could mean that you are relying on the perfect functioning of a backup system, or at worse there is no backup, and you are in an extreme condition immediately.

Any Turbo Propeller system needs care to ensure that Beta is not achieved in flight unless the aircraft has a certified mechanism to do so. Even so, they can have operational limits on such use.