It is always an extremely upsetting time when such an event takes place and we see so many times the consequences of flying in areas of severe thunderstorm activity or clear air turbulence. So what may have happened to Ethiopian Airlines Flight 409 which departed Rafik Hariri International Airport in Beirut 2:35 a.m. on a routine flight to Addis Ababa? Reports by witnesses have said the aircraft was on fire prior to going down. The only facts we know is that it disappeared from radar a few minutes after takeoff and crashed into the sea only 3.5 km offshore.
Almost all international airports operate sophisticated systems to detect regional thunderstorm activity, squalls or clear air turbulence. At the same time all modern aircraft carry extremely high tech navigational equipment, collision avoidance systems and weather radar to avoid the main cell activity in such storms.
The problem here is that we have a departing aircraft that is still fully under the control of the local Air Traffic Control (ATC). This control is split into sectors such as Arrivals, Departures and the Tower itself for landing and take off. The airports own radar is extremely complex and can not only identify each aircraft by its squawk code but also can monitor the surround weather very accurately. I myself worked in such an environment and used to play games with certain people by telling them it will rain on them in a few minutes time etc.
So what impact does such weather have on aviation and how do these very unique systems develop, especially in a coastal region that makes them so unpredictable. From the operational perspective we had a system whereby, as normal, the Captain is always in charge of his aircraft no matter what the circumstances. Having said that the Captain is fed information from ATC or from his own airline operations controller to help him decide his course of action. In my, case we in operations, always had a certain amount of persuasive control in order for the Captain to achieve the best options and make the final decision.
I have always held the greatest respect for thunderstorm which in weather terms is formed in cumulonimbus clouds (CB’s). I am sure we have all observed this huge cloud formation form and when they reach their full potential they look like a blacksmiths anvil in shape. They form fairly quickly and take on this shape and almost as quickly can die and fade away. If one watches these CB’s from a distance you can see a plume rise up from its centre where high energy pushes up through the normal flattened top…..sometime soon after this final burst of energy the storm cell starts to diminish as its internal energy escapes out the top of the anvil shaped cloud. The energy, force and condition that lie within such CB’s is remarkable and that is why in most cases aircraft take evasive action to avoid them or delay their departure or arrival if at all possible.
My policy always used to be, that if such a thunderstorm or CB was directly over the airport, I would ask the Captain to delay his arrival or to take up a position in the holding pattern….that is assuming he had enough fuel to hold for the duration.
So many accidents have occurred as a direct result of these CB’s being over the vicinity of the runway or alternatively a captain has flown his aircraft directly into the active cell of a CB without diverting from his track to avoid them. So lets now look at what these CB’s are all about, what lies within, how aircraft can be damaged and what normally happens in routine flight when one encounters these storms.
Inside of this huge CB’s are powerful forces at work. You have thunder and lightning, hail and tremendously powerful up drafts and down drafts that demand great respect. The ATC in Lebanon would have seen these on their radar screen and would have known the aircraft departure track as well as any on track CB’s.
When an aircraft is arriving or departing it is under the strict control of ATC. The pilot would have received a pre flight brief on the weather conditions whilst on the ground prior to departure. Upon take off he would have his weather radar operating that would have clearly seen the CB’s cells or hearts. This basically then comes down to two facts. ATC knew of the CB’s on track and so did the Captain. However, upon commencing the take off run and for a short time after take off the crew are at their highest workload until their departure checks have been completed. In this case with having thunderstorms close in to the shore this would have added additional workload to the crew.
Let’s tale look inside a CB and see what happens and also look at the equipment available on the aircraft and at the airport. An aircraft entering a microburst will encounter strong headwinds, followed by strong tailwinds, as it flies from one side of the microburst to the other. If the pilot compensates for the headwind (to decrease lift) a bit too much, then the aircraft will lose lift in the tailwind and quickly strike the ground/water. If the aircraft is struck by lightning this is then
dissipated through the aircraft and back into the atmosphere with the assistance of static wicks. Estimates show that each commercial airliner averages one lighting hit per year but one crash that was attributed to lightning strike was in 1967 when the fuel tank exploded, causing the plane to crash. Generally, the first contact with lightning is at an extremity...the nose or a wingtip. As the plane continues to fly through the areas of opposite charges, the lightning transits through the aircraft skin and exits through another extremity point, frequently the tail.
Aircraft are protected from lightning strikes by two things. The first and most important is by a good pre flight brief involving both weather forecasters and ATC and the other by the Captain in the avoidance of such powerful cells. The second is through a small unsung device called the "static wick". Obviously if the Captain is not aware or prepared and enters such a storm then it is possible for a catastrophic outcome or failure of aircraft components. Sometime within these cells the aircraft can encounter large hail particles and this again can result in damage to the aircraft.
As we already know aircraft have in the past disappeared such as the Air France A330-200 airliner over the South Atlantic on December 1 2009 which possibly encountered en route tropical thunderstorm activity or severe clear air turbulence. Many major disasters have also, in the past, been associated with thunderstorm activity such a microburst which is when a sudden down draft (as shown in the above diagram) hits an aircraft flying through it. Basically we all know that aircraft land into the wind but with such a microburst the wind can suddenly change into a downward blowing tail wind…..which unfortunately causes the aircraft to crash into the land or sea. One should always remain vigilant and sometime over cautious and avoid such storms whenever possible.
When an aircraft is flying from A to B it will pick up such weather on its radar and ask the controller to divert off its intended path until it has passed the storm and then return to normal track. ATC themselves frequently give out warnings and other aircraft flying in the region also pass on such vital information.
The causes behind the loss of this relatively new aircraft cannot yet be determined but the fact that it is in relatively shallow water will allow the salvage teams to recover the hull and missing victims as well as the black box……only then will the truth be known. On must also bear in mind that sabotage cannot be ruled out or a possible missile attack….all possibilities have to be addressed but sadly this could be a classic case of an aircraft flying into severe weather.
Before leaving the subject of weather and it effects on the aviation industry I need to explain the complications of coastal weather which is a combination of the normal passing weather systems and a locally derived weather that sometimes makes forecasting extremely difficult.
It can be very unpredictable and certainly local knowledge will sometime save the day. One very important weather factor is that created by the coastal effect that is unique compared to normal weather. You can have moist air drift in from the sea, it is then heated as it crosses the land and pushed up over the high ground to form thunderstorms which then drift back towards to coast. At night the reverse can happen when the sea gives of its heat and forms coastal offshore thunderstorm that can last for some considerable time. When all of this is mixed with the normal weather systems and you have a very complex picture. However with good equipment, vigilant Air Traffic Control and a good crew most of these disasters could have been avoided. As I said before at the moment we cannot blame any of these factors until the black box has been recovered and the circumstances leading up to the crash have been investigated.
I have included this chart to show that some time after the crash (which was at around 0235 local time) the offshore thunderstorms were still active. This satellite picture was taken at 0600 GMT which is 0800 local time in Lebanon.
Peter Eyre – Middle East Consultant – 26/1/2010