Zitat

Original von Balu der Bär
Engine Pressure Ratio

Zitat

EPR?

Zitat

Ermittler suchen weiter nach Unglücksursache

LONDON - Mehr als einen Monat nach der Bruchlandung von Flug BA38 in London Heathrow suchen die Ermittlungs- behörden weiter nach der Ursache für den Ausfall beider Triebwerke an der betroffenen Boeing 777-200ER. Fest steht, dass im Anflug der aus Peking kommenden British Airways auf Runway 27L in drei Kilometern Entfernung zum Flughafen und in einer Höhe von rund 200 Metern zunächst das rechte und wenige Sekunden später auch das linke Triebwerk herunterfuhr.

Beide Rolls-Royce Trent 800 Maschinen sprachen weder auf eine vom Bordsystem initiierte noch auf eine manuelle Gasannahme an. Eine entgültige Erklärung hierfür liegt weiterhin nicht vor, obwohl den Ermittlern der Behörde für Flugunfalluntersuchungen AAIB ein weitgehend erhaltenes Flugzeugwrack und die Aussagen beider Piloten zur Verfügung stehen.

Das Szeanrio eines vollständigen Schubausfalls stellt in der zivilen Luftfahrt ein sehr seltenes Ereignis dar. "Derartige Zwischenfälle sind in der Regel lediglich bei einem Ausgehen der Treibstoffreserven denkbar", kommentierte William Voss, Vorsitzender des Flight Safety Network. Wenngleich BA38 mit 10.500 Kilogramm noch über hinreichend Kerosin in ihren Tanks verfügte, setzt an dieser Stelle eine erste Theorie der Ermittlungsingenieure an.

Eine an den Treibstoffpumpen beider Triebwerke ausgemachte Ablagerung könnte zum Trockenlaufen der Maschinen geführt haben. Doch wirft dies die Frage auf, wie derselbe Fehler nahezu zeitgleich an zwei unabhängigen Systemen auftreten konnte. Die Wahrscheinlichkeit für den Eintritt eines derartigen Ereignisses musste in der Zulassung der Boeing 777 auf eins zu einer Milliarde minimiert und damit faktisch ausgeschlossen werden.

Zitat

The accident aircraft was a scheduled international flight from Beijing, China to London, England, and the flight was routine until about two miles from touchdown.

The engines would not respond to commands to increase thrust, and as a result the aircraft touched down about 1000 feet short of the runway.

There was a significant fuel leak, but no post-crash fire. All 136 passengers and 16 crew members were able to successfully evacuate the aircraft, and the most serious injury was a broken leg suffered by one passenger.

This latest AAIB update provided additional insights into the final moments before touchdown, the state of the fuel and fuel systems, and the condition of the engines and their associated control systems.

The damage caused by the landing gear had a direct role in the post crash fuel spill, and the report also showed how aircraft evacuation procedures contributed to the amount of fuel that spilled. Previous AAIB reports indicated that the engines did not respond to either autothrottle or autopilot commands shortly before landing. The latest report is a refinement of what was stated before.

The first officer took control for the landing at a height of approximately 780 feet, and shortly afterwards the autothrottles commanded an increase in thrust from both engines. The engines initially responded, but at a height of about 720 feet the thrust of the right engine reduced.

About seven seconds later, the thrust reduced on the left engine to a similar level. The engines did not shut down and both engines continued to produce thrust at an engine speed above flight idle, but at less than the commanded thrust.

The engines failed to respond to further demands for increased thrust from the autothrottles, or from the manual inputs of the flight crew. The airspeed reduced as the autopilot attempted to maintain its intended glide slope angle, and by the time the aircraft had descended to about 200 feet above the ground, the airspeed had reduced to about 108 knots. The autopilot disconnected at about 175 feet, and afterwards the aircraft descended rapidly, contacting the ground just inside the airfield boundary fence and about 1,000 feet short of the runway.

During the flight, the aircraft traveled through high altitude regions of unusually low temperatures, with the crew changing altitudes at one point to fly through warmer air.

British weather authorities noted that although the temperature was unusually low, it was not exceptionally low.

During the flight, the fuel temperature dropped to as low as minus 34 degrees Celsius. However, an analysis of fuel samples taken after the accident showed that the freezing point of the fuel was much lower, at minus 57 degrees Celsius.

The fuel was tested by more than one laboratory, and initial results found that the fuel showed no signs of contamination or unusual levels of water.

This report made no mention of ice or slush forming in the fuel or fuel system during any portion of the flight.

Examination of the fuel tank revealed a loose connection in one of the fuel lines. Small pieces of debris were recovered in both the left and right main tank, and in two fuel pumps. Debris was also found in the left engine fuel oil heat exchanger (FOHE).

Detailed examination of both the left and right engine high pressure fuel pumps revealed signs of damage that could indicate that there was either a restriction in the fuel supply to the pumps or that there was an excessive aeration of the fuel. In spite of the damage, both pumps were found to be still being capable of delivering full fuel flow.

This update did not conclude what role, if any, that these fuel system anomalies played in the accident. An examination of the engines indicated no evidence of a mechanical defect. Also, there was no indication of ingestion of either birds or ice.

An examination of the data from the electronic engine controllers (EEC) and the quick access recorder (QAR) revealed no anomalies in the engine control system.

The electronic engine controllers and fuel metering valves were found to have responded correctly following the reduction in engine thrust.

During the impact and subsequent ground roll, the nose gear collapsed, the right main landing gear separated from the aircraft, and the left main landing gear was pushed up through the wing.

The right main landing gear ruptured the rear right wall of the center fuel tank and penetrated the cargo hold. The two front wheels of the right main landing gear broke away and struck the rear right fuselage, penetrating the cabin adjacent to rows 29 and 30.

Damage from the collapse of the left main landing gear left the crew unable to close the left spar valve, while damage from the right main gear limited the crew's ability to close the right spar valve. Because of the way the evacuation procedure was executed, the crew could not close the right spar valve, and this contributed to the size of the fuel spill.

The evacuation checklist developed by Boeing for the 777 called for moving the fuel control switches to the cut-off position prior to operating the fire handles. This sequence would have allowed the crew of the accident aircraft to close the right spar valve in spite of the damage to the part of the electrical system that controlled that valve.

According the the AAIB report, a revised checklist from British Airways, for which Boeing had raised no technical objection, split the responsibility for moving the fuel control switches and operating the fire handles between the two flight crew members, and did not have any measure in place to ensure the correct sequence of actions.

During this accident, the fire control handle for the right engine was operated before the fuel control switch for that engine was moved to the cut-off position, keeping the spar valve in the open position and allowing fuel to escape.

AAIB noted that this situation was not causal to the accident but, could have had serious consequences in the event of a fire during the evacuation.

The AAIB recommended that Boeing notify all triple seven operators of the need to operate the fuel control switch to cut-off prior to operation of the fire handle, for both the fire drill and the evacuation drill, and to ensure that all versions of its checklists are consistent with this procedure.

I'd like to talk a bit about how the latest report addresses some of the more widely discussed possible causes of the accident.

There has been plenty of speculation about the causes of the accident by persons and organizations not connected to the accident investigation. One of the more prominent set of speculations was an article in the February 12, 2008 issue of the Wall Street Journal Online, which mentioned a buildup of ice crystals or slush in the fuel system as a possible cause of the engine thrust anomalies.

Nothing in the recent AAIB report directly supports that portion of the Wall Street Journal Online's article. In fact, the AAIB has not found evidence of any significant water contamination, and also found that the the fuel stayed well above its freezing point throughout the flight.

The Wall Street Journal Online article also expressed doubts that there would be any safety recommendations released with the next update to the investigation. In fact, the report, which was released six days after the article was published, did have the safety recommendation concerning the emergency checklists.

These significant differences between the speculation of the Wall Street Journal Online and the update from the AAIB illustrate the difficulty that any outsider has when it comes to drawing conclusions about an investigation that is still in progress.

The suggestions made in previous AirSafe.com podcasts about how to evaluate what's being published about this investigation are still valid and are worth repeating.

If you're interested in following what is said about the investigation online or in the news media, keep this in mind: prior to the completion of the investigation by the AAIB, those outside of the investigation, including aviation safety experts and the largest news media organizations, will have access only to a fraction of the relevant information.

The AAIB will likely provide several more updates prior to publishing a final report, and these updates represent the most authoritative sources of information about the ongoing investigation.

Finally, take the time to read between the lines and to figure out what is fact and what is speculation. For additional information and other resources related to this investigation, please visit 777.airsafe.org.

Zitat

Original von Balu der Bär
Finally, take the time to read between the lines

Zitat

Hätte das FADEC den eine Möglichkeit derart die Triebwerke runterzufahren, das keine throttle response da ist??

Zitat

Original von Emirates777
Die Maschine steht momentan noch vor dem BA Technik Hanger: Link

Die Streifen hinten lassen den Eindruck erwecken das die Maschine mit Tesa noch mühselig zusammengehalten wird...

Bin gespannt wann sie in die Schredder kommt.

Zitat

Original von Flugzeugschrauber

Zitat

Hätte das FADEC den eine Möglichkeit derart die Triebwerke runterzufahren, das keine throttle response da ist??

Ob bei dem Engine Typ das so programmiert ist weis ich nicht.
Aber beim CFM56 gibt es das. Wurde nach einem Zwischenfall so über die Software geregelt.
Bei dem genannten Zwischenfall, spulte ein Engine kurz vor dem aufsetzen auf full power hoch und überschoß dabei sogar die maximal erlaubte Höchstdrehzahl. Dabei trat eine starke yaw Bewegung auf, (was man sich wohl gut vorstellen kann )
Es wurde eine G/A geflogen, das Triebwerk über das Feuerhändle abgestellt und ein single engine app. geflogen.
Nach Untersuchung und Auswertung unter anderem durch den Hersteller, wurde die Software dahin gändert, daß in diesem Fall das Triebwerk in Flight idle geht.

Viele Grüße

Ps: Hier findet ihr den offiziellen Vorläufigen Bericht der Untersuchungsbehörde. http://www.aaib.dft.gov.uk/cms_resources...G-YMMM.pdf

Zitat

Weisst du den Unterschied zwischen EEC und FADEC?

Zitat

Ermittlungen zu British Airways Flug 38 dauern an

SEATTLE - Der US Flugzeugbauer Boeing wird in einem eigenen Testaufbau Untersuchungen zum Triebwerksausfall einer 777-200ER der British Airways am 17. Januar in London Heathrow durchführen. Das Unternehmen will die Bedingungen in den Treibstoffleitungen zu den Pumpaggregaten in mehreren Belastungsszenarien nachstellen. Dies bestätigte Boeing in einer Stellungnahme.

Eine erste Auswertung des Ereignisablaufs lege das Auftreten einer Störung in diesem Systemteil nahe. Möglich sei eine Verstopfung der Zuleitung durch Eiskristalle oder eine Verdickung des Treibstoffs in Folge sehr niedriger Temperaturen. Boeing arbeitet in der Versuchsreihe eng mit den Ermittlern der britischen Behörde für Flugunfalluntersuchungen (AAIB) zusammen.

Zitat

The crash of British Airways (London) flight 38 at London Heathrow Airport in January of this year could have possibly been caused by abnormally cold weather conditions over Russia, air investigators have now said. Experts have homed in on fuel flow as the key issue which led to the crash landing of the Boeing 777. The Air Accident Investigations Branch (AAIB) released a report saying that the drop in temperatures to -105°F (-76°C) may have caused the fuel in the aircraft to thicken during the flight. This translated in the aircraft being unable to get additional thrust required during the landing phase. Further tests are required to determine exactly what happened. In its report the AAIB has focused on the “region of particularly cold air” between the Urals and Eastern Scandinavia during the 10-hour flight from Beijing to Heathrow. It found that temperatures plummeted far lower than would have been expected for the region.

While the average freezing temperature of aviation fuel is -53°F (-47°C), tests showed that the fuel used on the airliner does not turn to ice until -71°F (-57°C). Tests also found that the fuel temperature throughout the flight never dropped below -29°F (-34°C). Even if the fuel had not become frozen it could have thickened to an unusual extent, which could have restricted its flow. Further testing on fuel is being carried out both at Rolls-Royce’s engine plant in Derby and Boeing’s factory in Seattle. A number of other theories have been ruled out by the AAIB that include birds flying into the engine or possibly ice blocking the engine intake.

Zitat

Eis im Tank wahrscheinlicher Grund für Bruchlandung

LONDON (dpa, aero.de) - Eis im Tanksystem war wahrscheinlich der Grund für die Bruchlandung einer Boeing 777-200ER der British Airways auf dem Londoner Flughafen Heathrow vor fast acht Monaten. Der Treibstoff habe vermutlich wegen des Eises wenige Minuten vor der Landung nicht zum Triebwerk transportiert werden können, heißt es in einem am Donnerstag vorgelegten Bericht der Untersuchungskommission zur Ermittlung von Luftfahrtunfällen.

Die Boeing 777 aus Peking war am 17. Januar auf Europas größtem Flughafen neben der Landebahn aufgekommen. Bei der Bruchlandung kamen die meisten der 136 Passagiere und 16 Besatzungsmitglieder jedoch mit dem Schrecken davon. Lediglich ein Passagier brach sich ein Bein, acht andere wurden leicht verletzt.

Schon kurz nach dem Crash war bekanntgeworden, dass die Maschine nicht den nötigen Schub von den Rolls-Royce Trent 800-Triebwerken bekommen hatte. Die zuständige Ermittlungsbehörde AAIB stellte klar, dass die Boeing 777 während des ganzen Fluges ausschließlich Temperatur- und Druckbedingungen ausgesetzt war, für die der Flugzeugtyp zertifiziert ist.

Eine Vereisung im Treibstoffsystem wurde als Erklärung daher zunächst als unwahrscheinlich zurückgestellt. An den Hochdruckverdichtern festgestellte Kavitationsschäden belegen jedoch, dass der Einspritzdruck an beiden Triebwerken schlagartig abfiel.

Der Bericht ist bereits der fünfte, den die Untersuchungskommission zu Flug BA38 vorgelegt hat. Die Ermittler regen eine Neuregulierung der Zulassungsvoraussetzungen durch die europäischen und amerikanischen Luftfahrtbehörden an. Unter einer solchen Maßnahme soll die Toleranz der Triebwerke gegenüber sich auf Langstrecken unter sehr kalten Umgebungsbedingungen natürlich bildenden Eises erhöht werden soll.