Aircraft system failures – Are they awful?

What happens during aircraft system failures?

I wanted to talk about something that has happened to me in the past before. Do you know what happens if we have aircraft system failures? No? Well let me talk about it for a moment or two.

I’m sure you’ve heard it said before. Flying is statistically the safest method of travelling. Here’s some boring stats stuff for you. In 2018, there were 160 recorded incidents, of which 13 were fatal. This accounted for the deaths of 534 people. Even more staggering, is that in 2017 there were no fatal passenger jet crashes at all. The only fatalities were from regional turbine propellor aircraft. This accounted for 13 deaths. Now let’s compare this to cars. The World Health Organisation states that over 1.25 million people die from road traffic incidents each year. So for 2018, cars contributed a staggering 233,982% more fatalities than jet and turboprop aircraft.

One of the basic principles of aircraft design, especially on commercial aircraft, is redundancy. This has a simple and basic meaning. If something fails, a backup will take over. This is one of the main reasons why flying is statistically one of the safest methods of travelling. So what happens if something on an airplane fails?

That time one of my generators failed

Not an aircraft IDG, but similar (although slightly more basic), layout.

A while ago, as we taxied out, one of the generators failed (IDG 1, which stands for Integrated Drive Generator 1). This was the generator on the number 1 engine (the one on the left side of the plane). Luckily this was still on the ground, so it wasn’t a big deal. That being said, we returned the aircraft to the stand and asked the engineers to come and have a look. Long story short, the engineers were unable to sort out the issue there and then. This meant that the aircraft had to be dispatched without IDG1. This was alright though, as we still had IDG2 on the second engine. We also had the APU generator available to us.

Most aircraft have multiple AC generators. The A320 has two engines, an APU (Auxilliary Power Unit) and a RAT (Ram Air Turbine). The APU is also a small turbine in itself. It’s solely designed to provide electrical power and bleed air to the aircraft when the engines aren’t running. Each engine and the APU have their own generators attached to them. The RAT powers an emergency generator that is only used in emergencies. So, in essence, we have four independent sources of AC electrical power, four generators. (Five sources if you count the Ground Power Unit. But that’s an external supply).

The APU comes in handy during aircraft system faults
An APU is basically a small turbine which is designed to provide electrical power and bleed air.

For normal operations, the aircraft must have two sources of AC power available. If we only have one source of AC power, we declare “MAYDAY”, and land the plane ASAP. In my situation, we had IDG2 and the APU generator available to us. This meant that we could depart, but the APU had to remain on for the entire flight. Not a problem at all! The only thing that we had to be aware of is the fact that the APU burns about 150KG of fuel per hour. Once we had factored this burn into our fuel figures, we were ready to go. Needless to say, everything went off without a hitch!

That’s one type of aircraft system failures. Let’s take a look at another.

That time my flaps wouldn’t extend

They say that once you transition from being a First Officer to a Captain, your first 100 hours will be filled with system issues. It’s not a fact, just a bit of pilot banter. This wasn’t the case for me, luckily. Instead, I had my issues during my command training! 

The one that I remember the most is my day 2 of line training. Let me set the scene for you. We were flying into Lublin airport, in the east of Poland. It’s not got the longest runway in the world, but admirable at about 2500 metres. Anyway, it’s a late winters night and the strong crosswinds are blowing snow right across the runway. This is creating what we call “blowing snow”. I’ve only seen it a few times, but it is a beautiful phenomena to behold! 

Story time

The guts of a wing flap/slat system
The flaps help aircraft to take-off, land and increase drag.

Anyway, as we’re getting ready to start the approach, I ask the trainer to select flaps one for me. This is to get the aircraft slowing down so we can land safely. 

“Oops”, I hear the trainer say.

I look at the flap indicator in the main panel. Would you believe that the flaps have got stuck! They have barely extended at all. Maybe a few degrees at most.

Well this is just great. Just what I need two days into my command training!

“Ok, my radios, QRH Checklist please. Flaps/Slats disagree.” This prompted my colleague to pull out the Quick Reference Handbook (QRH). This holds checklists for many types of known failures. 

Once we had gone through the checklist and were happy with our fuel, we had to make a decision. We went through our decision making process. Lublin wasn’t the best option for landing. The blowing snow, gusty crosswinds and not-too-long runway weren’t suitable for landing without flaps. 

So what did we do?

We decided that the safest option would be to divert to Warsaw, which has two runways available. The longest runway was almost 3700 metres long! This gave us plenty to concrete to be able to land and stop with a faster than normal approach speed. 

It was a while ago now, but on final approach, I remember the approach speed being about 185 knots! Also, even though our flaps were not working, we were able to extend our slats. These are the devices at the leading edge of the wing which also help us to fly slower. 

All in all, the approach and landing felt quite “normal”. The passengers were happy to be on the ground and were coached back to Lublin.

We found out that the issue had been with a single sensor. The sensor that monitors each flap to see if there is any asymmetry had failed. This meant that the flaps were unprotected from asymmetry and therefore refused to move. At least that’s what the engineer told us.

If you want to see a video of me landing with this failure, then there’s video on YouTube that a plane spotter recorded. Here is the link for it. As you will see, it seems like a pretty normal approach.

My flapless landing into Warsaw after diverting from Lublin. Video thanks to


There we have two separate stories about system failures that I have experienced while at work. Aircraft system failures do happen. As you can see, there’s not a great deal to them. Yes, they required a bit of extra thinking. Yes they were a bit of a nuisance. But at the end of they day, everything still had a sense of normality to it, and it was above all, safe. 

I mentioned redundancy earlier. This is definitely something that helps aviation to be so safe. But there is something else that adds to safety. This is procedure.

Airlines all have SOP’s (Standard Operating Procedures). These are set out so that every single pilot flying every plane will do (almost) the exact same thing. At any time in the flight, the pilots should be able to know what the other pilot is doing. This is because everything we do is set out and described in our SOP’s. 

Sometimes though, SOP’s do not contain everything we need. Sometimes, very rarely, something may happen that’s never been seen before. This is when technical knowledge is important. If a failure occurs, and there is no specific SOP for us to follow, there is something else we can do. We basically follow our checklists up to a point where they don’t cover what we need. We then systematically diagnose the situation based on our technical knowledge of the plane. This very rarely happens in aviation though, so honestly there’s no need to be worried.

Checklists help avoid situations that lead to aircraft system failures
Checklists and procedures are vital to safe flying


So that’s the deal. When things go wrong, we have backup systems available to help us transition from a failed state to a normal state. Aircraft system failures aren’t a huge deal 99% of the time.

Also, procedures help us keep in line with the company’s requirements, and this adds a robust level of safety. This is because we, as pilots, are all doing the exact same thing and flying the same way every day.

I haven’t gone into engine failures in this post, because I think that an engine failure is worthy of a post all in it’s own. I will do this post in the near future.

In the meantime, if you have any questions, please don’t hesitate to send me a message via the contact page here.

Also, please do follow me on Instagram here and TikTok if you search @TheHumblePilot. I also have a facebook page here.

I hope you liked the post, and I will see you in the next one soon.

Happy contrails!

The Humble Pilot