Question about flight diversions

[AmericanFlyer]

My CEO, who is a frequent flyer on Continental Airlines, swears that his flights from Houston which go on the regional jets are diverted much more often than other aircraft, say Boeing 737's. Is this really true? My speculation is that there is a required minimum amount of "extra" fuel that a commerical aircraft is required to carry in order to execute a missed approach and divert to the alternate airport plus some left over for reserve, but I wouldn't think an airline's policy would vary by aircraft type. Can someone who really knows answer with the correct information? Is my CEO correct or is he fitting the data to advance his hypothesis?

[AerocatS2A]

Impossible to say whats happening without knowing the reasons for the diversions.

You are correct about the requirements for fuel, it is dictated by the weather forecast at the detination airfield. If the weather is good then you won't require fuel to divert to an alternate (though the Captain may choose to carry it anyway.)

[AmericanFlyer]

Thanks for answering, Aerocat. I don't really know the details about why a particular flight was diverted, but what I am trying to find out is "Is the policy of an airline (Continental in this case) to carry extra fuel dictated by weather and/or the pilot, by aircraft type, or by some other factor?" There could be a lot of reasons, and it does cost money to tanker fuel around. On the other hand, it costs money to divert flights also. In other words, is the assertion that for Continental Airlines flights, are the regional jets diverted more often (if this is really a fact) because of something related to the aircraft type or not? Maybe it's just the capacity of the tanks, take-off or landing weights, or some other aircraft-specific factor that allow the freedom to tanker more fuel?

[Curious Pax]

A pilot will be able to give a sensible answer, but 3 items occur to me: possily higher spec on the Boeings allowing more CAT2 and higher landings; more experienced pilots on the Boeings so are able to do such landings; higher limits for such things as crosswinds on the Boeing due to its greater size.

[Wee Weasley Welshman]

Impossible to say BUT with a larger airline and type like a Continental 737 it is highly likely that both the crew and aircraft are certified to land in Cat3a weather conditions, i.e. thick fog.

Smaller aircraft at smaller airlines may not have the capability or have ticked both the equipment or pilot training boxes necessary to achieve Cat3a capability. So they can land in weather conditions better than Cat3a, i.e. moderate or light fog.

As fog is the biggest cause of diversions then likely this is the prime reason for the differing diversion rates.

Cheers

WWW

[AerocatS2A]

Thanks for answering, Aerocat. I don't really know the details about why a particular flight was diverted, but what I am trying to find out is "Is the policy of an airline (Continental in this case) to carry extra fuel dictated by weather and/or the pilot, by aircraft type, or by some other factor?"

What I meant by not knowing the reasons for diversion is that fuel may have nothing to do with it.

Are the aircraft diverting while half way to their destination in order to refuel, or are they getting to their destination and then having to divert to an alternate because the weather doesn't allow them to land?

The most common reason, in my experience, to divert, is that you get to your destination, conduct an instrument approach, find the visibility is not good enough to land, so you divert to your alternate. This obviously requires more fuel than not diverting.

As to your questions about fuel, I'm only familiar with Australian regulations, which state that the pilot in command is responsible to ensure that the aircraft has adequate fuel for the flight. There is then some guidlines that have been issued to advise an acceptable method of determining what "adequate fuel" means.

In short, for commercial jet aircraft, they are to carry enough fuel to reach the destination, plus 10% of that fuel, plus an extra 30 mins of "fixed reserve" which should still be in the aircraft after landing.

In addition to that, they are to carry enough fuel to get to an alternate aerodrome if the forecast weather at the destination is below certain limits.

There are also some other cases where extra fuel should be carried, and the captain may always choose to carry more fuel (within reason.)

These guidelines apply to all aircraft with a turbine engine, that includes anything that Continental would operate. So, assuming that the US has similar guidelines, there is no reason that any of the smaller aircraft would be carrying less fuel (relatively speaking) than a larger aircraft. And as I said earlier, most diversions use more fuel, so it's not generally something that happens due to a lack of fuel, but more due to weather (or a mechanical breakdown that requires an early landing.)

Having said all that, on a long flight, it is possible for the crew to find that they no longer have the required fuel to reach their destination (due to unforecast headwinds.) In this case, a return to the departure airfield or an enroute airfield may be required. But this would be relatively rare.

In all, it is most likely that the diversions are weather based rather than fuel based, and that the smaller aircraft are diverting more often because they don't carry the equipment to land in conditions of really poor visibility (as the others have said above.)

In case you didn't know, the cat2 and cat3 mentioned above are different categories of instrument landing system (ILS.) Essentially, with better equipment on the aircraft, a higher category of ILS may be flown which means that you may land with worse weather. The highest category, cat3, allows you to land with very low visibility such as you'd get with thick fog on the runway. Normally these are flown entirely by the aircraft autopilot including the landing.

[AmericanFlyer]

As you have pointed out, I omitted an important fact. My CEO says that when they arrived in the vicinity of the original destination, the aircraft flew in a holding pattern for about ten minutes, the pilot came on the intercom and said to the passengers that the flight was being diverted because he didn't have enough fuel to loiter around. Hope this helps.

[AerocatS2A]

Ok, that means they had fuel to get to their destination plus fuel to get to an alternate. They would have been required to loiter for various reasons including waiting for weather to pass through, or waiting for other aircraft to land. They may have had no gaurantee of a landing at a particular time so once they get down to having only enough fuel to get to the alternate (with a gauranteed landing), they took that as the safe option, rather than holding for an unspecified time and possibly running out of fuel (eek!)

That scenario could happen to an aircraft of any size as crews normally just take fairly close to the minimum flight fuel, so if they are required to hold for an unforeseen reason, they may have to divert instead.

The earlier information about aircraft equipment and instrument landings still stands. A larger aircraft equiped to cat3 standards would be less likely to have to hold for weather.

So I would still guess that if there really is a corellation between aircraft size and diversions, and it's not just coincidental*, it is more likely to be because the larger aircraft is better equiped rather than carrying more fuel.

There are also other factors that limit the fuel load. If an aircraft has a full load of passengers and baggage then they may be restricted to carrying the legal minimum fuel. A lighter load will give the crew more leeway to carry extra fuel if they want to. Again, that could apply to aircraft of various sizes.

*Such as your CEO has travelled on smaller regional jets to destinations that typically have poor weather and has travelled on larger aircraft to destinations that often have good weather. Or he's travelled in one during the winter, and the other in summer.