It’s time for another Ask Cranky. Today, we’re looking at an operations question from a reader.

How many extra planes do airlines keep on hand to fill in for maintenance issues that require longer than a day to fix? Or maybe a maintenance issue that is longer than a day to fix is very-very rare? I’d imagine that a small international carrier that flies a 747 on a route does not keep an extra 747 to fill in if they have equipment problems and that they delay flights or cancel and rebook on another route/carrier. However, it’s hard to imagine that Delta Airlines does not keep an extra few A320/737′s parked in Atlanta ready to go on a moment’s notice. So what is it like out there? How many extras do airlines generally have and where do they keep them?

Jeff Z.

It’s a great question, and it’s one that’s going to vary by airline. In general, the smallest airlines probably won’t have a spare on hand. It’s just too expensive to keep an airplane down, waiting for another to break if you’re so small in the first place. But as airlines get larger, they need more spares.

I remember when I worked at America West, we ran a terrible operation in the summer of 2000. Part of the fix was increasing the number of spare aircraft in the Phoenix hub to be able to recover more quickly when an airplane broke. (And they broke a lot back then.)

I went to US Airways and asked them about their spare situation today, and the answer was an interesting one.

Since we operate a “different” schedule each day the number fluctuates a bit.

Today for instance, we currently have 340 active lines of flying on the mainline operation. Here is what we have built into the schedule for spares:

13 spares total….

2 737’s (covering 300s and 400s), 7 Airbus (covering 319/320/321), 2 B757 (covering 757/767), 1 A330 (covering A330-200 and 300) and 1 EMB 190.

So there you have it. Each fleet type has at least one spare available, but it might not be an exact match. For example, if a 767 breaks, then only a 757 will be able to step in with about 25 fewer seats. During the off-peak winter season, that might not be as big of a problem as it may be during the packed summer season.

Every airline has a different philosophy on how many spares to keep and it will change within each airline. At America West, for example, when the airplanes were at a place where they became more reliable, they could look at reducing spares again.

There are a lot of different milestones that can be used to determine when a merger is truly complete. The one I always use is when you can no longer book a flight on both airlines. For United and Continental, that day comes this Saturday.

In the wee hours of early Saturday morning, United’s Apollo reservations system will be shut down in favor of Continental’s SHARES system. In fact, we’ll see a lot kept from the Continental side, even though the United name will reign supreme.

Beginning on Saturday, you will no longer be able to book a flight on Continental – they’ll all be on United. This is great news . . . not that the Continental name is disappearing but rather that there is only one airline to deal with. This means no more problems of working with two different airlines even though they’re really one.

Considering I spent over an hour trying to use a Mileage Plus member’s miles to upgrade a Continental flight last week, this piece of the merger couldn’t come soon enough.

Of course, the transition won’t be easy. It never is. The United reservations folks will now be forced to use an unfamiliar system. Training undoubtedly helps, but it’s still a big change. And then there’s the physical switch itself.

It is no small task taking all that reservation data, putting it into a new system, and then hoping it all works as planned. It’s never a perfect transition. Remember when US Airways and America West flipped the switch? There were a lot of problems.

So, if you’re flying United for the week beginning this Saturday, give yourself some extra time at the airport just in case. Here are some other things to keep in mind.

Reservations
Since the airlines are moving to Continental’s reservation system, it’s those record locators (confirmation numbers) that will survive. If you booked on United before the system switch, I would assume that there will be a mechanism for the new system to still recognize those old numbers when you try to use them. But if you had a split reservation with both United and Continental flights, you’ll be fine just remembering the Continental number going forward.

UPDATE: I just received clarification from someone at United that this is not quite what’s happening. Both United reservations and Continental reservations will be transferred into a new SHARES system, so there will be a new reservation number assigned to each reservation. If you have a reservation with both United and Continental flights, you will have three record locators: the old United one, the old Continental one, and the new combined United one. The key point? Any of them will work when you try to pull up your reservation.

The Website
If you’re one of the few people who love the not-so-affectionately nicknamed United.bomb website, then you’ll be sad to know that the Continental website is the survivor.

It’s really going to be a carbon copy of the current Continental website. For a pre-production version of the new site, head over to pss.united.com and you can play around.

MileagePlus
March 3 also will be the effective date of the new MileagePlus combined frequent flier program. If you have a Continental OnePass number, that will be your Mileage Plus number. If you have a current Mileage Plus number from United, then that’s toast.

If you had both and linked them, then you’ll just consolidate under the Continental number. If you never had a OnePass number, you’ll be getting a new one from United.

Patience is the key in the next couple weeks. If you’re flying United, it could be rough going as the systems combine, but in the end, it will be a much better experience since the airlines will operate as one.

There are more things to be merged, but most of those aren’t as visible to travelers. This is the big weekend.

Five things not to do on airplanes – CNN Out of the Office
This was fun to pick through five things people shouldn’t do on airplanes. I’m sure you guys have plenty to add to the list.

United Makes New First and Business Class Confusing—We Make It Clear – Conde Nast Daily Traveler
United has rolled out a fairly confusing new naming scheme for its premium cabins. Here’s how it breaks down.

In the Trenches: Dizzying Payroll Rules – Intuit Small Business Blog
Payroll is surprisingly difficult to deal with on your own, but I guess that’s why there are others who can help.

This became a big discussion on Twitter, so I thought I’d bring it here. In a couple months, my wife and I are taking the little guy on his maiden voyage, and we had the chance to upgrade using miles on a cross country trip. Would you do it with a newborn or not? It was a mixed bag on Twitter.

(We actually did do it, but of course, we’ll be incredibly conscientious about any noise.)

Have you been through Miami lately? Unless you’re an American Airlines-loyalist, the answer is probably a firm “no.” While American’s presence continues to strengthen, other airlines are running away in droves. The latest is Delta, which dropped its last attempt to make non-hub flying there work this week. Why is this happening? It’s actually a very clear lesson on how not to run an airport.

Miami is a vibrant city with a great local Latin population. That local presence combined with its location should make Miami a fantastic place for a Latin American hub. Sure enough, it is. It’s one of American’s jewels in an ever-rusting crown. By all accounts, it’s a rock star of an operation for the airline.

That makes sense, because soon enough, American and its oneworld partners might be the only ones left. Here’s a list of airlines that have left or cut back recently.

• Air Jamaica cut its recently re-launched route to Kingston (but it still does Ft Lauderdale)
• AirTran pulled all flights after the merger with Southwest
• Alaska recently decided to switch its flights to Ft Lauderdale
• Delta killed flights to Cincinnati, London, Memphis, Orlando, Raleigh/Durham, and Tampa
• KLM canceled summer service to Amsterdam and winter service for next year is up in the air

So what’s left? A lot of silver birds. While Delta pulled out of many cities, it’s not like other US airlines are stepping in to fill the void. Pre-merger United doesn’t fly there much – there’s only one flight a day from Denver and three a piece from Chicago and Washington, many on regional jets. US Airways flies to Charlotte and Philly but it doesn’t even bother with its Phoenix hub. It can be downright difficult to find good flights to Miami if you’re traveling domestically . . . unless you fly American.

From Europe, there will continue to be some service, but it’s highly seasonal (winter, of course) and leisure-based. Nearly every Latin airline has to continue to fly there because that’s the bread and butter route, but we’re increasingly seeing even Latin carriers look elsewhere. TAM now flies double daily flights to Orlando in addition to its Miami service. But it’s not Orlando that’s the real threat. It’s Ft Lauderdale.

Ft Lauderdale has seen a tremendous increase in service over the last decade, much of it from low cost carriers. Sitting only 25 miles north of downtown Miami, Ft Lauderdale is not that far, especially considering how much of the population lives north of Miami itself.

Spirit makes its home in Ft Lauderdale with low cost flights all over the US and the Caribbean. JetBlue has grown its operation there over the last few years, and the new Southwest/AirTran combo will have a significant presence. Allegiant bases airplanes there while airlines like Alaska have moved service over from Miami. And despite its stated desire to fly into primary airports, Virgin America picked Ft Lauderdale over Miami. What gives?

You can probably blame it on two things. One is American. American is a tough competitor, and it fights ferociously if anyone invades its turf. But that doesn’t explain everything. The one that really grabbed me was Alaska’s decision to leave. Alaska and American are long time partners and American even puts it code on the Alaska flight. So something else is happening here to push airlines away.

That “something else” is Miami’s out-of-control spending. The airport is on a building spree putting together incredibly expensive, long-delayed terminals that are causing costs to simply skyrocket. In 2010, the airlines paid roughly $17.61 for each passenger boarded. In the next decade, that will balloon to over $30. Think about that. How can a low cost carrier survive in an environment like that? It can’t. And Alaska, despite not being a low cost carrier, apparently feels the same way. Everyone should. The crushingly high costs are simply too much to overcome, even with a partnership with American.

Of course, high costs alone wouldn’t cause the exodus. But high costs combined with a convenient alternative? Ah yes, that’s enough to make waves. It’s very easy for airlines to walk away from Miami and its money-wasting ways because Ft Lauderdale is so close. By comparison, Ft Lauderdale is downright cheap. In 2010, its cost per enplanement was a measly $5.32. You can imagine why low cost carriers have flocked there. That airport itself is going to see costs rise as it works to build a new runway for almost $800m (just broke ground), but even if costs tripled, it would be half of Miami.

Of course, if costs triple, Spirit and Allegiant might find themselves running away, so hopefully Ft Lauderdale is able to keep its spending down and its charges low. If the trend continues, we might just find Miami renaming itself to Miami oneworld International Airport.