Sticking Elevator Actuator Seals cause

QANTAS Flt QF72 plunge-dive Upset

Possibly the seals had not been changed per the Airworthiness directive (see below)

Julian Walsh, director of aviation safety at the Australian Transport Safety Bureau, said an on-board electronic centralized aircraft monitoring system indicated there was "some irregularity with the elevator control system."

The aircraft departed from its normal flight at 37,000 feet, climbed 300 feet, "then as the crew were responding, the aircraft pitched down quite suddenly and rapidly," he said.


"Certainly, there was a period of time when the aircraft performed of its own accord," Mr. Walsh said.


The aircraft, built in 2003 and operated by Qantas since then, made an emergency landing at a remote airfield at Learmonth, an Australian defense force air base, near Exmouth, in Western Australia state.
Ref: the AD for servo solenoids

Interesting reading the AD that has been issued for the A330's elevator solenoid valve o'rings. The part installed as standard are MS28775-xx. They are allegedly not suitable for 'Skydrol' or other phosphate ester based hydraulic fluids. In fact they are only suitable for fuel and hydrocarbon based hydraulic fluids. They can also be found in use for sealing against the elements.
The AD replaces them with NAS1611-xxx seals that are specifically designed for 'Skydrol' type fluids.
Could that have been the fault?
[PDF]

Airworthiness Directive - AD/A330/37 Amdt 2 - Elevator Servocontrols

File Format: PDF/Adobe Acrobat - View as HTML
For elevator servocontrols installed in damping position on A330-200 ... (b) If the seals installed have PN MS28775-XXX or a PN that cannot be ...
www.casa.gov.au/airworth/airwd/ADfiles/over/a330/A330-037.pdf
 
EASA AD = this link
 
This Airworthiness Directive concerning A330 elevator servo controls mentions O-rings on solenoid valves of each servo, and the timing of the AD is the same as in the Herald Sun article

http://www.comlaw.gov.au/ComLaw/Legi...30037Amdt2.pdf
see also this link

Change from active mode to damped mode is obtained by means of a

mode selector which is controlled by two identical solenoid valves

housed on the servo control. The sealing of each solenoid valve is

ensured by four O-ring seals.

During pre-flight control checks, the flight crew of an A330-200 observed that one of the elevators was blocked in down position, the

ECAM screen displaying “F/CTL PRIM 1 PITCH FAULT”.

This situation was due to two independent failures, one of which was hidden, which occurred on one of the elevators.

Investigations revealed that the origin of the blocking of the elevator in down position was due to the inability of the Yellow servo control to switch to active mode.

This inability:

- was caused by an internal hydraulic leak due to the deterioration of an O-ring seal on a solenoid valve,

- was not detected by the PRIM 2 computer and not announced to the flight crew.

Incorrect PN for solenoid valve O-ring seals in IPC:

An incorrect O-ring seal PN in IPC 27-34-51-1 could have led to the installation of O-ring seals incompatible with the hydraulic fluid causing them to deteriorate within several flight hours.

In both cases, this situation if not detected could lead to the loss of an elevator on takeoff and, in the extreme case, reduce the controllability of the aircraft which is potentially critical.

The aim of this new AD is to :

- take over the requirements of AD F-2004-158,

- render mandatory the terminating action for § 1, 2 and 4 of this AD

by introducing new capped seals on solenoid valves for A330-200

only.

from this link


 

Media Release 2008/40b

Qantas Airbus Accident Media Conference

10 October 2008

 

The Australian Transport Safety Bureau investigation is progressing.

The aircraft's Digital Flight Data Recorder (DFDR), Cockpit Voice Recorder (CVR) and Quick Access Recorder arrived in Canberra late on Wednesday evening. Downloading and preliminary analysis has revealed good data from both recorders. Data from the FDR has been provided to participants in the investigation which include Qantas, the French accident investigation authority - the Bureau d'Enquêtes et d'Analyses (BEA), Airbus and the Australian Civil Aviation Safety Authority. The aircraft's operating crew acted responsibly and promptly after the aircraft was shut down by isolating the CVR to preserve information for the purpose of the investigation.

While the full interpretation and analysis of the recorded data will take some time, preliminary review of the data indicates that the aircraft was cruising at 37,000 feet, when the aircraft initiated a climb of about 200 feet, before returning back to 37,000 feet. About 1 minute later, the aircraft pitched nose-down, to a maximum pitch angle of about 8.4 degrees, and descended about 650 feet in about 20 seconds, before returning to the cruising level. About 70 seconds after returning to 37,000 feet there was a further nose-down pitch, to a maximum pitch angle of about 3.5 degrees, and the aircraft descended about 400 feet in about 16 seconds, before returning once again to the cruising level.

I turn your attention to the screen where there is a very basic animation, using data from the Digital Flight Data Recorder, of the first pitch-down event.

Detailed review and analysis of DFDR data is ongoing to assist in identifying the reasons for the events. At this point, the event appears very complex. The aircraft contains very sophisticated and highly reliable systems whose interaction is very complex. As far as we can understand, there seems to be issues with some on-board components. Further examination of the auto-pilot system, data sources used by flight control computers and the flight control computers themselves, along with the interaction of the flight crew with the aircraft's systems is necessary to achieve a better understanding of the event.

Meanwhile, the on-site team in Learmonth is working hard and has assessed and documented significant damage to some overhead panels, consistent with injuries that were sustained by the aircraft occupants. Ceiling panels were removed and wiring looms were visually inspected and no defects were found. In addition, visual inspection of the aircraft has been conducted and no structural defects have been found. Inspection of the cargo area found all cargo was loaded in the correct position and no load shift was evident. All of the cargo load was properly secured.

With all necessary precautions taken and completed to ensure no loss of evidence, the aircraft was then powered up and data pertaining to specific computers and systems was downloaded. This was done in a careful and methodical manner to ensure no data was lost. This data is essential to the investigation and includes additional information not recorded on the Digital Flight Data Recorder. This download occurred on the aircraft involving representatives of the ATSB, Qantas and Airbus. This data is currently being analysed. More data is to be downloaded today and further assessment will be carried out on the aircraft's systems. It is likely that a number of components will be removed for further downloading/testing, some of which will need to be done at the manufacturers facilities in France or relevant country of manufacture.

Ongoing activities include a detailed review of the aircraft's maintenance history, including checking on compliance with relevant Airworthiness Directives, although initial indications are that the aircraft met the relevant airworthiness requirements. Work is also ongoing to progress interviews, which will include with injured passengers to understand what occurred in the aircraft cabin. The ATSB plans to distribute a survey to all passengers. There is no evidence at this stage to indicate that the use of portable electronic devices by passengers contributed to the event, however, it would be expected that questions relating to such usage would be included in the passenger survey.

The nature of the initiating event has not yet been determined. The investigation will be examining the broad range of factors that influence the operation of the aircraft. There was been close, frequent, communications between the ATSB, Qantas, Airbus and CASA. That close communication will continue as the investigation progresses to ensure that any necessary safety action can be instigated as soon as possible should critical safety factors be identified.

The ATSB will release a Preliminary Factual report within about 30 days, however, should any critical safety issues emerge that require urgent attention, the ATSB will immediately bring such issues to the attention of the relevant authorities who are best placed to take prompt action to address those issues and will publish such information more broadly ahead of the Preliminary report.

As I noted in the media conference earlier this week, we cannot pre-empt the findings in relation to cabin safety issues and the wearing of seatbelts, but this accident does serve as a salient reminder to all people who travel by air of the importance of keeping seatbelts fastened at all times when seated in an aircraft.

Animated representation of relevant recorded data

An animation of the incident was prepared using Insight Animation software. A file containing the animation in Insight View format (.isv) is available for download from the ATSB website. This file requires the installation of an Insight Viewer that can be downloaded from www.flightscape.com/products/view.php at no charge.

Media Contact: George Nadal: 1800 020 616

Related Documents:Audio of media conference 10 October 2008 (2.6 MB - mp3) | Animation of media conference 10 October 2008 (5 MB - isv) |


Qantas jet's plunge sparks speculation about pilot over-correction on flight to Perth

RETURNING home after visiting his fiancee in Singapore, Tim Ellett found flight QF72 from Changi to Perth began like the 12 other trips he had taken before.

The Airbus A330-300 jet that carried Mr Ellett and the 302 other passengers is one of the most technologically advanced planes in the world. It is also reputed to be one of the safest.

But three hours after takeoff, the jet plunged 650ft, injuring 50 passengers, some seriously. And it has now emerged that the calamity has striking similarities with two previous incidents, including an emergency involving a Singapore Airlines flight in 1996.

In these cases, questions were raised about the design of the A330's cockpit, including whether it could lead to both pilots, instead of just one, inadvertently overcorrecting the plane, resulting in the plane's computers recording a double input.

Settling in for the four-hour flight, Mr Ellett, 22, watched a movie and kept track of the trip via the flight path map on his television screen. The woman passenger next to him slept.

When the plane was only about an hour away from Perth, the journey turned into an extraordinary experience. The jet was soaring over the Indian Ocean, 110 nautical miles north of Carnarvon on Western Australia's north coast, when it suddenly and inexplicably climbed 200ft.

This slight rise from the jet's 37,000ft altitude went unnoticed by many of the passengers and crew, but aviation experts believe moves would have been under way in the cockpit to discover why the aircraft had risen.

The plane returned to cruise normally, but about a minute later, passengers were suddenly hurled up to the cabin ceiling as the plane plunged 650ft in 20seconds. As bruised and battered passengers, many crying and screaming, clambered back to their seats, the jet levelled out and returned to cruising at 37,000ft. But 70 seconds later, the jet dropped another 400ft for 16seconds, creating havoc.

The plane then made an emergency landing at Learmonth airport, near Exmouth.

Investigators from the Australian Transport Safety Bureau said yesterday there was no evidence of pilot error but they were examining data transfer between pilots and onboard equipment.

In 1996 a Singapore Airlines A340-300 -- which has an identical cockpit to the A330 -- suffered a "severe upset" over central Australia

Sq A340 - 1996

The Captain decided to balance the fuel [ showed his lack of knowledge] by turning the hyd. pumps off [ 2 at a time]. They were not protected in those days as Airbus thought no one would be that stupid.
With no hydraulics to the stabilizer, it caused a violent pitch-up. Quick thinking F/O grabbed his side-stick and commanded a full down input. while el Capitano realized his mistake and quickly put the hyd. pumps back on.
Result was a wild ride with some injuries, don't know how many, but not as bad as this A330 upset.

 after crew inadvertently switched the hydraulic pumps off, forcing the aircraft to pitch up. A violent plunge followed when both pilots took a corrective action simultaneously.

According to an Airbus pilot who spoke to The Weekend Australian, the Airbus flight computers algebraically assess information, and if both pilots take the same action in an emergency situation, often due to instinct, the effects can be doubled.

This is exacerbated by the cockpit layout, in which the pilots' joysticks are positioned at either side of the cabin; at the left hand of the captain, and the right of the co-pilot.

In the Singapore Airlines case, according to the Airbus pilot, both pilots pushed forward on their joysticks to correct the jet's altitude. The pilot said another airline had suffered a similar upset in the late 1990s, where dual pilot input doubled the effect of the downward pitch motion.

In the 1996 incident, nine passengers and three crew were injured, and like the Qantas incident, the emergency was originally reported to be caused by turbulence.

The bureau's Aviation Safety Investigation director Julian Walsh described the event as very complex. "As far as we can understand, there seems to be issues with some on-board components. Further examination of the auto-pilot system, data sources used by flight control computers and the flight control computers themselves, along with interaction of the flight crew with the aircraft's systems is necessary to achieve a better understanding of the event," he said.

Qantas would not comment on whether a double input could have contributed to the emergency and said all maintenance checks were up to date.

Australian Manufacturing Workers Union national secretary Dave Oliver said members were very concerned about damage to the airline's reputation.

Mr Ellett said he would soon be back on the route. "It could have happened to any airline," he said.