Airbus Law, Protections and Stabilities

I want to start this post by talking about the Airbus A319 tasked with bringing the Olympic torch and flame to England from Athens. This specially painted A319 was given the name “Firefly” and assigned the flight number BAW2012 for obvious reasons. I have to say that I’m not a fan of this special Olympic livery, for me it looks like they decided to paint the aircraft and gave up three quarters of the way through and the actual design just feels uninspiring. The word “Firefly” under the captain side window could be seen to be peeling off when the aircraft was parked up on the apron indicating the money that has been spent putting the design onto the aircraft and yes I’m probably being overly critical but I just feel if you’re going to do a job, do it well. At least the landing was good!

Today was our second full motion simulator lesson, it was supposed to be yesterday however the simulator we were supposed to be using decided to break before we got into it. For some reason the computer wouldn’t allow the gear to be locked down and despite rebooting it, it just wouldn’t work. Very strange that a parameter cannot just be modified but I think there must be a computer chip that runs that particular function that’s faulty.

One of the most defining characteristics of Airbus aircraft, that sets it a part from other passenger jets, is that it has 3 different laws that govern the operation of the aircraft. The laws are – Normal, Alternate and Direct.

Normal law is the law that is active 95% of a pilots flying time. With it comes various protections that have been put in place to increase safety and reduce a pilots workload. There are 5 types of protection in normal law, high angle of attack, high speed/low speed, load factor, bank and pitch. It also auto trims the aeroplane so that when you set an attitude on the artificial horizon, it will keep that attitude.

I won’t bore you with how each protection works but lets just say that each one keeps the aircraft operating within it’s limitations and allows the pilot to quickly react to certain situations such as terrain avoidance without fear of over stressing the aircraft, like you could on a Boeing.

Alternate law comes about when flight control computers go down, with it you still have the load factor limitation however your other protections are lost and instead you get stabilities. These stabilities help to keep the aircraft operating within its normal speed range by makings subtle changes to the pitch attitude to either keep the speed up or reduce it. The difference between stabilities and protections is that stabilities can be over ridden so extra care would need to be paid when in alternate law. There is an alternate law without the low speed and high speed stabilities however you will still get load factor stability.

Direct law occurs when you have a triple system failure, and when the landing gear goes down in alternate law. The side stick deflection commands direct deflection of aileron and pitch as opposed to a load factor or roll rate experienced in normal law. There are no protections available at all. Despite the amount of system degradation involved the aircraft is surprisingly responsive in control, perhaps a little too twitchy although that could easily be just because of the way the simulator has been programmed.

We also looked at some more single engine work and a rejected take off with emergency evacuation just for fun!

I have to say, I’m really enjoying learning to fly the Airbus and the motion isn’t causing me as much discomfort as it did in the first full motion simulator lesson. The taxying motion is horrible though, it really throws you around, I’m sure it can’t be like that in real life otherwise the cabin crew wouldn’t be able to prepare the cabin or maybe we are just really bad at taxying! I just think the way the Airbus works is so clever, the ECAM, the protections and laws etc, it appeals to the computer geek within me.

I’ve got a late simulator tomorrow so I think I’ll treat myself to a lay in!

From the cockpit on hydraulic stilts,


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