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An all things aviation blog

Monthly Archives: July 2012

If you have connected in DFW on AA you know it can be an interesting experience. The airport layout of a series of semi-circle terminals is designed to move people from the parking lot to the gate in the shortest period of time. It’s not designed to be a hub. It was in-fact the last major airport designed before airline deregulation in the 1970’s. In the 1970’s airlines flew set routs at set fees. This is much the way Southwest Airlines operates today, but I’m wandering off the point. After deregulation set in the hub-and-spoke model was developed and perfected.

The hub-and-spoke model allows airlines concentrate resources at a limited number of airports in the country. This allows airlines to spend very few resources at airports where they have limited flights and spend a great deal where they have a lot of flights. This is in an attempt to capture economies of scale. However, there is something that people and I think that airline managers forget, and that is path dependency. Path dependency is simply this, the decisions we make today affect the decisions we make tomorrow. An example of this would be education, whatever, degree a person chooses is their life path. Changing that path is difficult, which is why people don’t do it that often. This path dependency effects the development of airlines.

Let’s apply path dependency to hub development and destruction. Hubs have both profitable and unprofitable flights. Profitable flights are great and I am not interested in those. Let’s look at the unprofitable flights. United has announced they are going to cut Houston-Paris. Ok the flight is unprofitable, there for the airline should cut it. Maybe. United has great analysts that tells them who is on the flight are they connecting or just arriving in Houston. These analysts tell United that any given flight maybe in the red, but if there is sufficient connecting traffic to flights in the black then it can be kept. Here is where the analysts go wrong. There is always going to be someone connecting on any given flight. Now when United cuts that flight, that passenger is simply gone.

But wait you say, the other flights are profitable and with the unprofitable flight gone United will make more money. Yes, but no. This idea is called “shrinking to profitability” and guess what it’s never worked. Why? Path dependency.  With those connecting passengers gone, those other profitable flights are less profitable. Due to the lack of service, there are no some flights that were profitable, that become unprofitable. Those flights get cut and so goes the airline down the path.

Now every hub has theoretical limit on both ends. Now Charlotte-to-Houston will never support A380 service, but it will support some level of origin/destination service. Now, we know strictly connecting hubs with no level of origin/destination traffic will not support a hub. Memphis and Cincinnati are examples of that. But cutting without replacing service is starting down the path to the death of the hub.

What can airline planners do then? If the route is never profitable, then cutting it will be the only option. However, let us add a question; where can the hub grow service to replace the eliminated connection service that would also be profitable? There are a lot of untapped markets out, give them a try.

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On June 1, 2009 Air France flight 447 from Rio to Paris fell from the sky over the Atlantic Ocean killing all 228 passengers and crew. Today July, 5th 2012, the final report on the accident was released by the BEA the French aviation authority. This report containing numerous recommendations represents the final word on what happened.

What happened? Well if you have seen the Nova film on the matter, then you have a good idea. If you haven’t you should. I’ll do my best to explain.

Cruise flight in a modern aircraft occurs at high altitude. Makes sense the higher the altitude the less air, the easier it is to move the aircraft through space. The downside is the aircraft has to be going fast enough to move enough air over the wings to generate lift.

Thus, infinite speed infinite altitude right? No.

At those speeds going though air is like going through soup. The aircraft causes disruptions in air. Too fast and these disruptions break the flow of air over the wings causing a high speed stall. Too slow, it stalls, too fast it stalls. The speed in-between is called the coffin corner. 20-30 knts either way at altitude and the aircraft stalls.

How do you measure speed. Well, at cruise flight speed is a function of pressure. The aircraft needs to know how much pressure is pushing against the front of the aircraft. They use pitot tubes. The measure pressure.

In this case the pitot tubes iced over. Thus the aircraft was unable measure pressure. So AF447’s electronic brain concluded that the pilot should fly the plane.

Ok, so if you don’t know the speed, you eventually stall and then you die.

No. If that were true there would be a lot fewer planes around. Airbus built in a setting where the aircraft will be airworthy. 85% power and 5 degrees nose up and the pilots will be able to control the aircraft.

If this is true why did AF447 crash? Well the pilots didn’t fly the aircraft. Imagine this.

You’re a commercial pilot, you’re 3hrs in to a 10hr flight. The flight is going smoothly, systems seem ok, dinner was just finished, and through a combination of food, stability, and slight tiredness, you’re not as alert. You know the majority of incidents happen on takeoff and landing, so there is not much to worry about. Oh and it is pitch black outside and inside. Then all hell breaks lose. Lights are now flashing on the control panels, audio alarms are going off proclaiming multiple emergencies, and you have no idea why all of this is happening.

The purpose of these alarms were to draw the attention of the pilot. The pilots of AF447 were both fairly junior. The senior pilot was having a rest. This is standard procedure for all international airlines. However, here the situation went from fine to catastrophic in a matter of seconds. The pilots did what anyone would do, panic.

Panic is something good airline crews plan for. It’s called crew resource management. Step one of the plan is secure oxygen. Step two is fly the plane. Step three is assess the situation. Step four is take appropriate steps to remedy the problem. Granted this is an over-simplification but it works here.

The crew on AF447 didn’t fly the plane. They got so caught up in alarms, systems, and other things, they panicked and forgot how to fly the plane. Nova showed what to do, set power and trim, fly the plane, then listen to the alarms.

Wait listen to the alarms is last? Yup, the pilots have to fly the plane. But the pilots are not all to blame here. (Though I think they are ultimately responsible)

Airbus shares a lot of the blame. People talk about the pitot tubes and that it was a parts failure. I call bull on this. Planes are designed to fly after an engine explodes, a pitot tube failure should not bring down a Cessna 152 (Do Cessna 152s have pitot tubes?) much less an Airbus 330.

Let’s take an engine explosion. Qantas Airbus 380 flight from Singapore to Sydney had an engine compressor explosion after leaving Singapore. Plane returns safely to Singapore, no fatalities. In documentary about this flight one comment the pilot made interested me a great deal. He mentioned having to go through an acknowledge pages of alarms on his data screen as well as the rest of his control panel. He stated that he spent a lot of the emergency not dealing with the emergency but acknowledging that there was a problem. As if he didn’t know from the engine explosion.

I think Airbus is overloading pilots in emergencies. Rather then encouraging the pilot to focus on flying the plane they are providing the pilot with too much information about the situation. I want my pilot flying the plane, no acknowledging a system prompt in the first few moments of the emergency.

Where the line is between too much and too little information, nobody knows. However, with fewer alarms would the AF pilots been able to save the flight, I think so.

Whatever happens now and in the future this sad chapter in aviation history closed.

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