This post is the second part in a three part series about some of the major causes of diversions. In part one I talked about weather diversions. In this part the focus will be mechanical diversions. Just like part one I will start off with a small scenario and then talk about procedures regarding mechanical diversions.
Imagine you are on a flight and everything is cruising normally. All of a sudden it gets quieter and you feel that the aircraft is slowing down and turning. After a few minutes the captain gets on the intercom and says: “Ladies and Gentlemen, sorry to tell you but we are going to have to stop short of our destination. We lost all oil pressure and quantity in the right engine and we have shut it down to prevent any further damage. As you probably can tell we just descended and we turning away from Chicago towards Cleveland to land there. Airplanes are made to fly on one engine and the copilot and I are trained in handling the situation. We will be on the ground in about 15 minutes. Just to let you know, when we get on the ground there will be emergency equipment out to meet us on the runway. I requested this just as a precaution just in the very unlucky event that anything should happen. Again, I’m very sorry about this but will be on the ground in 15 minutes. Flight attendants please prepare the cabin.”
The diversion I just described above is very rare. Jet engines are very reliable pieces of equipment and they are well maintained. Engines also get changed after a certain amount of hours so they do not fail enroute like this one, but all mechanical things can fail.
I have had to dispatch a scenario just like the one above. It was an afternoon shift later in the evening and the crew called up on the radio. They had lost all oil quantity and pressure in the right engine and had shut it down. They were right over the top of Norfolk, Virginia. I told the crew that they needed to divert to Norfolk. I briefly told them the weather was good and I would be contacting the local station to let them know that they were coming. It took the flight about 15 minutes to get on the ground. Once on the ground the captain called me, he said that their engine had blown oil all over the place and it was pooling on the ramp below the engine. Obviously, this was a major mechanical failure of that engine. I found out the next day that the engine blew a seal.
Engine failures are so rare that an airline pilot can go his whole career without actually having an engine failure. This has been my only engine failure in the 8 years I’ve been working as a flight dispatcher. Other dispatchers in my office have worked over 30 years and never had an engine failure on any of their flights. While an engine failure is the most obvious reason to divert an airplane, there are some other subtle things that could cause an airplane to divert for maintenance as well. Some of these could be issues with the fuel pump, air-conditioning packs, potable water issues and several others. These concerns, while not directly impacting passenger safety, may affect the ability of the aircraft to proceed to its next destination. It is always wise to address the issue before it becomes a matter of safety or canceling flights.
Mechanical problems happen often on an airplane but they are usually very minor and only the pilots and dispatchers know about them. There is a book on every airplane that gives detailed instructions on the procedures the pilots need to follow in case any of the systems has a mechanical failure. My airline calls this book the Quick Reference Handbook or QRH. Some airlines might call it by a different name but the purpose is the same. Most of these mechanical failures just require the crew to fly the aircraft in a different configuration and continue to the destination without any problems. Some of the procedures in the QRH have the words “land at the nearest suitable airport” This means the crew needs to land as soon as possible and the safety of the flight is in jeopardy.
The QRH procedure for the engine failure scenario that I described above has that phrase in it. Some of these other mechanical problems also carry the “land nearest suitable” verbiage:
- Cracked windscreen
- A single source of electrical generator power
- Any sort of fire
- Pressurization failure
- Engine fuel leak
- Crew oxygen system low
The QRH procedure doesn’t always have to say land at the nearest airport to make the plane divert. There are many times where it would be safe and legal to continue to our destination but instead we decide to divert somewhere and have maintenance look at the aircraft before we continue; as in some of the situations I mentioned earlier. This happens a lot on our transoceanic flights. There are many times where there might be a mechanical problem with an airplane and we choose to stop along the coast before heading across the ocean- imagine a potable water issue that is not addressed before heading over the ocean (not good!). We know we can only get the plane fixed or change to a different aircraft before heading over the ocean. Being careful ensures the safety of all involved and also makes sure the return flight does not cancel.
As you can see there are many things that can cause a flight to divert due to mechanical reasons, they all might not be as severe as an engine failure but when we feel that the safety of the flight is in danger it is always better to put the aircraft on the ground somewhere.
Tomorrow in part three I will cover passenger related diversions.