Qantas Airliner Plunges Out of Control.



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.

The US Federal Aviation Authority have now issued an Airworthiness Directive (AD) concerning the problems with ice in the fuel system of Boeing 777-200 and 300 airplanes fitted with Rolls Royce Trent 800 engines. The AD requires the crew to monitor the fuel temperature within 3 hours of top of descent and if it is below a certain temperature they must increase the engine power to prevent the formation of ice in the main tank fuel supply system. They can do this by stepping up to a higher altitude or increase the airspeed. There is no requirement to carry out this procedure if the aircraft is not fitted with Trent 800 engines.

There is also a procedure for the circulation of the fuel on the ground by a certified mechanic to prevent the formation of ice.

This AD is a result of the problems encountered in January 2008 by a British Airways Boeing 777 which failed to respond to a command for increased thrust while the aircraft was on approach to London Heathrow airport and landed short of the runway. the interim report suggested ice formed in the main fuel tank supply system during low fuel flow conditions in cruise flight. This ice then dislodged and caused a restriction in fuel supply during high flow conditions during approach.

No doubt there will be more measures to prevent the formation of ice from the engine and aircraft manufacturers but in the mean time the FAA are counting on this procedure to prevent the recurrence of the fuel restriction and loss of engine power.

British Airways Boeing 777 Crash at Heathrow

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 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 Airlines Maintenance 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 Woes

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.

Memorable Trip

A couple of days ago I came across a program on Discovery about the first commercial jetliner in the world. It was the De Havilland Comet and they had a lot of problems with it. There were a number of mysterious crashes where the aircraft just broke up in the air with no warning and plummeted from the sky with no survivors. Not the best of starts to the jet age.

After exhaustive testing, including submerging a full size aircraft in a specially built water tank and forcing water in and out of the cabin to simulate pressurization, the problem was discovered. The skin was to thin and the windows and doors square shapes caused stress to build in the corners and cracks to form. These cracks gradually grew until the fuselage failed and the aircraft broke up in flight. This was the first documented aircraft failure from metal fatigue and the start of the balancing act between strength and weight which is still being played out today.

Another reason I watched the show was a sentimental one. The Comet was the first aircraft I flew overseas on when I was in the RAF. That is dating me but I don’t think I mind anymore. We were on our way to Peru from England and I had expected to go in a Britannia which was a four engine turbo prop but to be going in one of the five Comets that the RAF had was a real treat.

When we had boarded the ‘treat’ turned into a slog with a fuel stop in Shannon, Ireland and another in Gander, Newfoundland before the overnight stop in Washington DC. The next morning suffering from an underestimate of the strength of the American beer we boarded and headed for the island of Jamaica.

The airport staff also was surprised by the Comet and we spent fifteen minutes dying from the heat, trapped on board as they ‘rushed’ Jamaica style to find a set of steps to get us off the aircraft. After a couple of hours we were on board again for the final leg to Lima in time for the evening meal, if only we had learned Spanish. Still for a nineteen year old the trip was memorable and ten weeks in South America and the return in the Britannia were even more so. But that is another story.

What if I Can't Swim?

Air Canada Jazz, the regional feeder airline for Air Canada, has just announced that the Life Preservers will be removed from all flights as a weight saving move. This is, of course, another way of saving precious fuel. But what about the customer’s reaction? Well, an airline always treats their customers like non voting shareholders who pick up the tab for anything the airlines do. This is just another example of an airline doing something without due regard to how it will be received by the travelling public. The announcement was not thought out in regard to the reaction from the rule ignorant public being whipped into a frenzy by the headline hungry press!

It is now common knowledge from the on going press coverage that Life Preservers are not required on the Jazz flights due to the fact they are not over water for the required distance.

This is not the only savings in weight that is being carried out throughout the industry. There are changes in cutlery, magazines and even the amount of water on board to flush the toilets. One airline has changed the size of the wine bottles to save weight.

With the price of fuel, bad economy and the shrinking of people’s real wealth, the reductions in everything but the actual ticket price will continue.