Airlines PNG Dash 8 fatal crash in PNG
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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.
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.
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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. 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?
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.
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.
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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.
) 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?
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.
Yes, the beta-lockout should be mandatory worldwide! No arguments there!
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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)
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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!
EDIT: This was done on Dash 8 300's in case anyone was wondering.
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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
Widerøe's internal investigation report (in Norwegian): Widerøe: Widerøes granskningskommisjon: Ingen feil på Wid...
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
Scary incident, no doubt. Is this what happende with the Airlines PNG Dash 8? Only with both engines?
"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
Widerøe's internal investigation report (in Norwegian): Widerøe: Widerøes granskningskommisjon: Ingen feil på Wid...
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
Scary incident, no doubt. Is this what happende with the Airlines PNG Dash 8? Only with both engines?
Last edited by Skipskatta; 16th Nov 2011 at 22:11.
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).
:|
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.
§ 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.
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.
§ 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.
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Did the official report really say that or is the explanation of the noise imagined by the press ?
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
divide by zero
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.
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.
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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.
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.
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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
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
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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.
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.
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.
This was done on Dash 8 300's in case anyone was wondering.
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.
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.
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.
From my knowledge there is still nothing to suggest that the crew pulled the levers through the gates, hence this is why there is still all the speculation I guess.
I also agree totally with what BBN Radar has said, obviously we drink the same beer in the same country !
I also agree totally with what BBN Radar has said, obviously we drink the same beer in the same country !
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DME arrival into Madang requires a 2x profile due to the Finistere range.
Would throttle lever be at that flight idle gate in descent any time before Madang?
On days before this day did it fly same profile and no problem?
