Aircraft News Weblog

Category: Uncategorized

  • Q400 Landing Gear Collapse

    Photo by Rafael Minguet Delgado on Pexels.com

    A Q400 aircraft landing at Halifax International Airport in Nova Scotia suffered a landing gear collapse after an uneventful flight. The Transportation Safety Board initial report found that the aircraft had a tire failure on takeoff. Upon landing, the tire remnants started rotating. This caused enough vibration for the main landing gear to unlock and collapse.

    When the propeller contacted the runway the blades broke off and the engine was badly damaged. The aircrew declared a Mayday and secured the aircraft for an emergency evacuation on the runway. All passengers and crew successfully left the aircraft with no serious injuries.

    As the investigation continues I would like to describe the configuration of the landing gear on the Q400. On the Down selection, the gear doors open. The main landing gear is hydraulically lowered aft from the engine nacelle. The Actuator linkage travels overcenter and locks, the landing gear doors then close again. It is held in the down position by hydraulic pressure and large springs.

    The Q400 is over 25 years old and is no longer in production. It is operated all over the world and has proven to be a reliable aircraft. The failure of the landing gear due to tire remnants vibration is not a new problem. It is unlikely the investigation will call for major modifications as a solution to this accident.

  • Q400 Landing Gear Collapse: Causes and Impact

    A Q400 aircraft landing at Halifax International Airport in Nova Scotia suffered a landing gear collapse after an uneventful flight. The Transportation Safety Board initial report found that the aircraft had a tire failure on takeoff. Upon landing, the tire remnants started rotating. This caused enough vibration for the main landing gear to unlock and collapse.

    When the propeller contacted the runway the blades broke off and the engine was badly damaged. The aircrew declared a Mayday and secured the aircraft for an emergency evacuation on the runway. All passengers and crew successfully left the aircraft with no serious injuries.

    As the investigation continues I would like to describe the configuration of the landing gear on the Q400. On the Down selection, the gear doors open. The main landing gear is hydraulically lowered aft from the engine nacelle. The Actuator linkage travels overcenter and locks, the landing gear doors then close again. It is held in the down position by hydraulic pressure and large springs.

    The Q400 is over 25 years old and is no longer in production. It is operated all over the world and has proven to be a reliable aircraft. The failure of the landing gear due to tire remnants vibration is not a new problem. It is unlikely the investigation will call for major modifications as a solution to this accident.

  • Spirit Airlines Pressurization Problems

    A Spirit Airlines flight out of Detroit was forced to turn back shortly after takeoff on Friday due to possible loss of cabin pressure, the airline said.

    Flight 417 took off at about 6:30 a.m. local time from Detroit Metropolitan Airport en route to Fort Lauderdale-Hollywood International Airport in Fort Lauderdale, Florida, Spirit Airlines said in a statement.

    Not long after takeoff, the flight turned back to the airport and landed safely “following a possible loss of cabin pressure,” it said. No injuries were reported.
    It was not immediately clear what had indicated a loss of cabin pressure or exactly how long into the flight the issue became evident. Airline officials were not immediately available to provide additional details.
    People identifying themselves as passengers on the flight posted photographs of themselves to social media with bright yellow oxygen masks affixed to their faces. The masks, which prevent the lightheadedness and unconsciousness cabin pressure loss can result in, are typically deployed during cabin pressure issues.

    (Reporting by Laila Kearney; Editing by James Dalgleish)

  • Continental Airlines Dash 8 Aircraft

    dash-8The tragic accident of the Continental Airlines Dash 8 has generated a lot of speculation about the role of ice in the loss of control and subsequent crash of the aircraft. I am not going to suggest any cause of the accident as there are many knowledgeable people involved in the investigation that will come up with the answers.

    I would like to explain to those who are interested, why ice makes such a difference in the handling of the aircraft.  To understand the problem you have to have an idea of the theory of aircraft flight.

     The wings have a shape which produces lift as they travel through the air. However, they also produce drag and they have a weight that is a gravitational force.  The weight of the wing acts through the centre of gravity; this is the point that the wing would balance on if it were removed from the plane. The centre of lift is where all the lift forces could be measured and  opposes and is normally behind the center of gravity. Because it is behind the centre of gravity there is a twisting force to lower the front of the wing. If this were not opposed then the aircraft would not be able to fly.

    The tail is the place where the opposition is generated. The tail surfaces are designed to generate a downward force to oppose the twisting force of the wing and keep the aircraft level.  So, everything is in balance.  There are times when more lift is required, for the aircraft to take off or fly slower so it can land.  To achieve this flaps on the back of the wing can be lowered to increase the size of the wing and produce more lift.

    When the flaps are lowered the centre of lift moves rearwards and the twisting force of the wing increases, this is normally opposed by moving the trim on the tail to increase the opposition force and raise the nose. There is a range of trim available which is sufficient for normal operation.

    This is the way the aircraft is designed to operate. When ice collects on the wings it changes the shape of the wing so that some of the lift is lost, it also increases the weight of the wing which can move the center of gravity forward.  The build up of ice on the tail will add even more weight to the aircraft and reduce its ability to oppose the twisting force on the wing. The result is the same as lowering the flaps without the added lift that would be generated. The nose would be lowered and  the way to deal with this would be to trim the tail to increase the downward force.

    This is exactly what the autopilot does. As the ice builds up on the wings and tail the autopilot trims the tail to increase the downward force. This can be a very slow and insidious process as the autopilot will use more trim to keep the aircraft level. If the crew are not aware of the situation they may find that the trim limit has been reached before they  know they have a problem.  If they then change the status quo by lowering the landing gear or the flaps the auto pilot will be unable to trim the aircraft and will disengage leaving the crew with a very dangerous nose down attitude for which instant recognition of the problem and the correct response will be needed to avoid a loss of control.

    This situation is normally also at low altitude and airspeed and is very hazardous. Most operators regard icing very seriously and when in icing normally instruct the crew to fly the plane manually to make them aware at an early stage of the amount of trim they are using to control the attitude. They can then decide if they need to climb out of the icing conditions or take other action to avoid increasing ice build up. There are different systems on different aircraft which either prevent ice forming (anti-icing) or remove it as it forms (de-icing). De-icing that uses air to inflate boots to distort the leading edge of the wing and break up the ice which has formed was the system on the Dash 8 in Buffalo. This system requires the ice be allowed to build up to a certain thickness before the boots are inflated as thin ice will not break off. An automatic timer will inflate the boots periodically and there is a manual system if the automatic periods are too long.

    The tragic loss of the aircraft in Buffalo has brought the problem of icing into the spotlight but aircrews and airplanes have been dealing with it ever since flying began and there are many safeguards built into the system. I hope this has shed some insight on the hazards of ice on aircraft and the means to combat it.

  • There is Hope for Diamond Owners

    The following article must be good news for Thielert powered Diamond aircraft owners after months of indecision.
    Diamond certifies Austro AE 300 turbo-diesel

    Diamond Aircraft has received European type certification for its turbo-diesel Austro AE 300 engine, a development the company says “secures its future.”

    Diamond had been scrambling to develop an alternative to the Thielert Centurion 2.0 turbo-diesel engine after Thielert filed for bankruptcy in April last year. The Centurion powers more than 400 DA40 piston singles and more than 500 DA42 twins. Diamond has not ruled out offering a Thielert option on future aircraft assuming the company recovers after a pending sale.

    “The complete program developed into one that was significantly more complex than originally anticipated,” says Diamond CEO Christian Dries of the certification effort, which ultimately took 42 months to complete at a cost of  €48 million. Dries says there are already 27 DA42 NG aircraft powered by AE 300 engines on the production line and type certificate for the aircraft is expected “imminently”.

    Dries says Diamond next will certify the engine as forward-fit for the DA40 and DA50, and will develop an AE 300-powered version of the DA42 multi-purpose platform. The company will also offer a retrofit version for its existing Thielert diesel-powered aircraft.

    So if all goes well those diesel engined dreams of avoiding all the problems with traditional engines may be alive again.Austro Engine

  • Fly By Wire

    Well it looks like the science fiction is being overtaken by reality. Recently a Gulfstream 550 jet was controlled by a light signal from the cockpit to one of the flying controls. The controls of an aircraft are traditionally moved by the pilots commands being transmitted to the control via a stainless steel cable or aluminum rods. This also involves pulleys and bellcranks to move the cable in the correct direction. Then ‘fly by wire’ was developed which relies on electrical signals to move the control surfaces. This saved weight and allowed computers to control the aircraft without the traditional cables.

    Now we have a signal from the pilots controls changed into a light pulse which is transmitted via fiber optics to a receiver where it is converted back to an electrical signal to move the control. This saves even more weight and is a lot more reliable than an electrical wire which can short or break. There is no danger of losing the signal if even a fraction of the fiber optic cable is left intact after it has been damaged.

    If you think this is ground breaking then you will be amazed to learn that in the same experimental aircraft there was a ‘fly by wireless’ system operating as a back up which as the name suggests has no connection from the cockpit to the control except a radio signal. This has to be the ultimate in weight saving and reliability. When it is fully tested and approved it will be almost unheard of to lose control of the aircraft due to mechanical or hydraulic failure as the systems will not rely on them.

  • Qantas Jet Plunges out of control. Updated

    A terrifying headline to all who fly in aircraft and it is a very real risk in the age of modern air travel. The infrequency of this occurrence is thankfully rare and the majority are weather related and avoidable.

    So, what went wrong with the Qantas Airbus A330-300 aircraft? During the flight the aircraft had several departures from its assigned altitude, the result of these changes were injuries and panic in the cabin as people who were not wearing their seat belts were thrown around.

    The majority of modern aircraft are flown by a fly by wire system; this is in response to the development of flight control computers which control the aircraft’s altitude and direction of the flight. These computers are designed to keep the aircraft within its design limits. If the aircraft is going too slow, too fast, or approaching the design limits it will take action to correct the situation.

    So, how does the computer know whats going on? There are sensors on the aircraft which measure the outside air temperature, air speed, altitude and angle of attack, (the amount of nose up or nose down), all these inputs, and many others, are sent to an Air Data Inertial Reference Unit (ADIRU) which converts them to signals for the Flight Computer so they can operate the flight controls the way the pilots require. 

    On the Qantas aircraft the ADIRU gave incorrect data to the Flight Computers which made the aircraft climb to reduce an incorrect overspeed and then dive to avoid a non existent stall due to low airspeed. The aircraft autopilot was engaged until the unexpected climb when it disconnected and the crew flew the aircraft themselves. Even though the crew was flying the aircraft the inputs from the ADIRU still continued to affect the aircraft. The design of the system is to keep the aircraft within its limits and the ADIRU was giving erroneous information to the Flight Control Computer that these limits were being approached. The effects were minimised by the crew but they were still bad enough to cause inuries to people who were in the cabin.

    This is the first known occurrence of this type of failure with the ADIRU.  Airbus have issued a Telex to all the operators of this type of aircraft to provide operational actions to minimise the effects in the event of this happening again. There are 3 ADIRU’s and 3 Primary Flight Computers on the aircraft control system and the investigation will now concentrate on how a failure with one had such an effect on the aircraft.

     

    Update

    There has been another similar incident with a Qantas Airbus A320 in the same area as the one noted above. This is an area where strong military radio transmitters are in use. There is a growing suspicion that the radio transmissions may interfere with the operation of the auto pilot. In this latest case the pilots were able to control the aircraft and return to there departure point.

  • British Airways Boeing 777 Crash at Heathrow – Report

    Ice has always been the enemy of aircraft, it builds up on the wings and reduces lift and it lies on the runway and reduces braking and directional control when landing, but now there is a new hazard. After nine months of investigation the Air Accidents Investigation Branch (AAIB) have decided the cause of the British Airways Boeing 777 landing short at Heathrow and crashing was due to ice in the fuel. All the passengers and crew escaped the aircraft with only minor injuries apart from one man who broke his leg.

    It has been known for years that there is water in aviation fuel and when the temperature drops, due to the aircraft operating at altitude, ice crystals form in the fuel. There have been chemical and mechanical solutions to this problem and it is a largely unknown problem in large commercial aircraft.

    The fuel passing through a Trent 800 engine like the one that was powering the BA aircraft goes to an oil/fuel heater in the engine fuel system. This takes hot oil from the engine to a matrix of small pipes and passes fuel around the pipes on its way to the fuel control unit and the burners. This is normally sufficient to melt any ice that may be in the fuel so it will not interfere with the operation of the engine. The theory of the investigators is that ice formed before the engine oil/fuel heater and reduced the amount of fuel available for the engines to use.

    The High Pressure fuel pumps that are downstream of the oil/fuel heater showed evidence of cavitation. This is a condition that happens when the impellor of the pump has an insufficient fuel supply to boost to a higher pressure and mechanical damage is caused to the pumps. Clearly there was low fuel supply to the engines but where was the restriction? Because of filters, low-pressure pumps and valves that are all in the fuel supply system it has not yet been determined as to where the problem lies.

    Why it occurred is also a mystery as there has never been a case of fuel starvation due to icing in the fuel system of a commercial airliner. The Flight Data Recorder has shown that within 6 seconds both engines reduced power to a value below that needed to maintain flight and the automatic systems and the pilots took the required actions to supply more fuel but to no avail as it could not get to the High Pressure Pump.

    The low fuel flow at cruise power settings on an especially cold, long flight may have caused a build up of ice in an area in the fuel system which, with the high fuel demand in the landing phase of flight, detached from its location and caused the restriction. This theory has not yet been proven despite extensive and imaginative testing. The reason it is being put forward is every other scenario has been eliminated. As this is a preliminary report we will have to wait some time, maybe years, before the final report is issued and the cause is known. In the mean time the FAA and the manufacturers of the engine and aircraft are going to look at ways to mitigate the effects of long, cold flights on the fuel system.

  • Qantas 747 Aircraft Maintnenance Problems

    A Qantas 747 en-route from Singapore to London which had to land at Frankfurt with an engine shut down due to a vibration warning is the latest incident to plague the airline.

    The recent explosion that resulted in a large hole in the side of a Qantas Airlines Boeing 747-400 has been confirmed to have been caused by a failed emergency oxygen cylinder.  This is believed to be the first occurrence of a cylinder failure on board an aircraft. The manufacturer of the cylinders requires the cylinders to be removed from the aircraft and undergo hydrostatic testing every 3 or 5 years depending on the model. Providing Qantas have kept to the schedule they cannot be blamed for the failure. 

    There have been several more incidents with Qantas aircraft in the last two weeks which has brought the harsh light of public scrutiny to the airline. A Boeing 767 had to return to the airport when fluid was spotted coming from the aircraft on take off by Air Traffic Control. This turned out to be an hydraulic leak. The other was a Boeing 737-800 which had an open undercarriage door after the landing gear was selected up after take off. Another hydraulic leak from the nose wheel steering system closed the runway at Sydney for40 minutes while the oil was cleaned up.

    Was this a series of coincidental faults or an indication of an underlying problem with the maintenance of the aircraft?  To my mind an airline with a safety record second to none and unrelated incident on different types of aircraft would suggest the former.  Qantas and the Australian Aviation Authority have a Safety Management System in place which other countries, including the US and Canada, are still aiming to achieve. It consists of a program of self assessment, risk analysis and investigations into incidents which ensure lessons are learnt and the probability of a repetition of the events is minimised.

    However, the Qantas airlines flight attendants have requested assurances from Qantas management that there is nothing wrong with the aircraft and these incidents are coincidental. Also, the Australian Aviation Authority has begun a two week assessment of Qantas to ensure the safety systems are at work in the company. The mechanics spokesman has said they have always done the best work possible but are now doing it while subject to budget restraints.

    Third party maintenance is a sticking point with the mechanics that fear the standards they are aiming for will not be achieved by sending the aircraft to Hong Kong and Malaysia for heavy maintenance checks. A 767 had to be grounded on return from Malaysia recently with over 90 snags.  The aircraft that suffered the explosion is expected to be back in service in November 2008 at a cost of $10 million.

  • Zoom Airlines Financial Troubles

    News today about Zoom Airlines which operates flights between Canada and the United Kingdom (UK) has run into financial problems. An aircraft was taken back from Zoom by the owner who leased the aircraft to them. This was after the Calgary Airport refused to refuel them as the bill owed to the airport authority was in excess of $400,000. A little while later the airport authority in Glasgow, Scotland refused to allow a Zoom aircraft to leave because the Civil Aviation Authority in UK had outstanding bills from the European Air Traffic Control agency (Eurocontrol) that had to be paid. 

    Zoom Airlines has now filed for creditor protection in the UK and Canada as they have a financial plan in place to sort their cash flow out which 95% completed. If the protection is granted by the courts the airline will continue to operate and the passengers will not be left holding worthless ticket.

    Many of the airlines in the world have been in Protection from the courts in the last few years and have managed to survive. This is now part of the business plan of airlines in the world of rising fuel prices and competition for passengers. We can only hope the airline survives and all the jobs with it are not lost.

     

    Update
    Zoom Airlines has now stopped operations. The airline management say that the actions of the creditors prevented them from continuing to fly and therefore the decision has been made to stop all further operations. The company apologises to all the passengers and more than 600 employees who are now out of work.