One of the advantages (or disadvantages, depending on how you see it) of my employer is that our airplanes are in many different places and therefore we change our place of work very often – I enjoy being in different spots as it never gets boring, but depending on your lifestyle it could be very annoying as well. Right now I am in Stockholm for the week, but I will be flying from Oslo again in July.
Today I am supposed to fly a morning ‘rotation’ (aviation language for a series of flights, in this case flying to the destination and then returning after a short while on the ground, typically around 45 minutes). When I checked the documents I noticed that one electrical generator is ‘deferred’, i.e. not working. It is very common to have ‘deferred items’ with practically all airlines. As commercial airliners are very complex machines it is unrealistic to avoid occasional component failures. Depending on the place and type of failure replacing the component immediately would mean major delays, great inconvenience to the passengers and massive costs to the airline. This is (among other reasons, most importantly safety) one of the reasons why airplanes are built with a lot of redundancy [1]. Many flight critical systems only need one component of a certain type to operate correctly, but the manufacturers usually install one or two backup systems. Even after their failure it would still be possible to fly the airplane to a safe landing, but would likely require a diversion. To regulate this airplane manufacturer publish a so called ‘Minimum Equipment List’ which needs to be approved by the authority [2]. The manufacturer needs to prove that a failure of a specific component will not reduce safety by analysis and tests (if the component is too critical it would be classified as ‘no dispatch’, i.e. the item would need to be fixed before the flight). There are also time limits until the defect needs to be rectified, in most cases 10 days, but there are other intervals as well. There may be additional limitations as well. The electrical system of the Airbus is very redundant. When everything is working normally two engine-driven generators generate the power for all systems, but one generator is able to take all the load. In addition there is also a similar generator that is driven by the ‘Auxiliary Power Unit’ (APU) [3], a small gas turbine in the back of the airplane. Normally the APU is shutdown in flight and is only used to generate electricity on the ground when the engines are shutdown. One generator (either an engine generator or the APU generator) is able to generate enough power to supply the whole network. In the highly unlikely event that all three generators fail at the same time there is an air-driven emergency generator (a small propeller under the fuselage) that, when deployed, can supply the essential loads so the airplane can still be controlled and landed [5]. With this amount of redundancy, safe operations can still be assured if one (of the three) generator is not working, but it requires some maintenance checks before each flight. There are also some items that we have to consider. If an engine driven generator is not working the APU needs to be running throughout the flight and we need to consider the additional fuel consumption in our calculations.
We decide to take some additional fuel for weather and decide to start boarding. Today we also have an animal among our passenger, a guide dog for a blind person. These kind of animals are allowed in the cabin. After a while we finally get on our way towards our sunny destination. We have an unusual routing today, leading us through the area controlled from Kaliningrad. It is the first time that I fly into Russian airspace. Unfortunately we are flying within a cloud layer so there is not much to see and it is also rather turbulent. Shortly before landing I make an announcement to the passengers informing them about our landing time and also that they can expect a lovely day, as its 26°C already and it’s still morning.
After landing we disembark the passengers and start fueling. We don’t have much time to enjoy the sunshine as our departure time is getting closer.
We prepare everything and after some new passengers are on board it’s time to head back to Stockholm. Austrian airspace is very busy today and we see a lot of airplanes, however it is very difficult to get a good picture due to the high speeds involved. I show the First Officer some small tricks that can be helpful. The clouds over northern Europe have disappeared and we get some gorgeous views of northern Poland and later on Sweden.
Coming into Stockholm is a little bit turbulent – the winds are not so strong and the terrain is not really rough, but in summer is common to have to ‘thermals’ [4] if it is warm. The First Officer, who is Pilot Flying for this flight makes a very good landing and at the gate we are already greeted by the next crew who performs the afternoon flight. After a short talk about the technical status and the weather we move back to the hotel. The generator should probably be fixed during the night by the maintenance engineer. All in all, a lovely day at work.
[1] Center of Gravity
[2] Fuel Planing
[3] Mount Teide
[4] Noctilucent clouds
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