How Many Extra Airplanes Does An Airline Need? (Ask Cranky)

Ask Cranky

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 Ask Crankyhave 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.

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38 comments on “How Many Extra Airplanes Does An Airline Need? (Ask Cranky)

  1. Cranky-

    I presume that these “spares” are ready to fly planes that are there in the case of breakdowns etc.

    How many extra planes are needed (or alternatively, what percent of the time, over the lifespan of a plane, is it out of service for) the overhauls- the B/C/D checks? I know a lot of these checks (the A checks?) can be done overnight on some planes, but I would presume that the more detailed checks take longer.

    Also, how much do these checks cost? Wikipedia states that the cost of the D checks is high enough that many older aircraft are taken out of service upon reaching their next D check mark, is this true?

    On another related topic, how many “spare” (on call, reserve, whatever you want to call them) pilots and FAs are required, relative to the ones scheduled to fly that day?

    1. I think the answers to some of these have already been covered, but for the rest, I don’t really know the answer. Heavy checks are expensive, but airlines don’t retire airplanes when they come up for their first heavy check. There does come a time, however, when the airlines decide that the aircraft are getting close to the end of their time anyway and a heavy check is a reason to retire them.

  2. This is one of the advantages of the Southwest model. At least twice I’ve been on WN flights where we boarded, were alerted of maintenance, and then about 30 minutes in were told by the captain that we were all going to move to the plane sitting at the next gate. I was even on a PHX-BHM flight that diverted to Albuquerque for MX and after about an hour they found us another plane to “steal”, boarded it, and continued on. Sounded like we would have spent the night if they didn’t have that flexibility.

    1. Robbing Peter to pay Paul. That plane at the next gate either had a later departure time or possibly less passengers to inconvenience by taking that plane. Another advantage to the Southwest model, is the cockpit can be flown by all pilots, whereas, other carriers have different types of aircraft, a mixed fleet of Boeing, Airbus. Hence, different cockpits.
      Spares are generally only found in hub bases. So, if your flight breaks down, downline, the above happens more often, you steal an aircraft instead of using that spare, which isnt near the mechanical.

      1. Reminds me of a MX problem right after boarding DEN-SNA. Was told aircraft couldn’t operate and head down to another gate.

        That plane was about to board to another city (midwest I think) which I’m assuming was less profitable and wouldn’t have as many logistical repercussions.

        They were just about to start the boarding process. We all sort of looked down (at least I did) as we trundled past them right onto their AC.


  3. One thing about spares is that they may actually be “maintenance spares.” These are planes that have required maintenance that can either be deferred or finished quickly to get a plane back on line. Perfectly good airplanes typically don’t sit around as spares, they get put on the line so a broken airplane can be sent to the hangar. Those hangar bound airplanes that aren’t so broken as to be un-airworthy are the larger part of your spares.

  4. Your chances are better if you are at an airlines hub and your planes goes out of service. There are always planes going in and out of maintance for different reasons and not every plane comes in and departs 30 minutes later. Some are kept on the ground a few hours before their next flight and could be used if the airlines knows they can fix something on one plance to use it in place of the other.

    1. True about hubs. I’ve been lucky twice when a spare was available immediately: AA at ORD and AWA in PHX.

  5. When I went to L.A. a few years ago, the Contenental flight I was taking switched planes at the litteral last minute. They had a spare ready to go right across the concourse & it was no big deal. Of course when the anouncement was first made to swich gates, there was a lot of grumbling.

  6. How about a “virtual” spare. The plane is assigned flying for the day, but at a greatly reduced rate, like an early morning flight and not another one until later in the day. If needed, it is put to use instead of sitting idle. Then the broken plane or another one is used later to cover the flying left open when the virtual spare was put to use.

    1. AFAIK this is what FedEx used to do, but they put their virtual spare up in the air flying a zigzag flight plan that got it near major spots where they have planes that could break down.

      I’ven’t heard about that for years, so I figured they’ve ditched this due to fuel prices.

  7. Whenever possible, that “virtual spare” is turned into a full spareby assigning the very early/late flying to another plane that normally starts late or ends early. in a fleet of 200+, we’ll be lucky to have 3-4 usable spares (read: not in heavy checks) scattered around the country.

  8. Cranky,

    Did the Sand Castle give you a break down of the number of Airbus spares on the East and West sides of the operation? I’m also going to assume they have 1 757 on each side of the operation as a spare.

    1. No, they didn’t. You’re probably right about the 757s because in the West, there are no other airplanes that can fly to Hawai’i. Probably worth having a spare for that, even if it is a very small fleet size.

  9. Remember back in the day, the late Eastern Airlines Shuttle kept spares on hand in DCA,LGA and BOS? They did it in case of a plane going tech and promised to pull an aircraft in cause there were more butts than seats on any given departure. That must have cost a pile of $$$$.

    Very cool topic Daddy B…thanks for the insight!

    1. They actually had extra planes sitting around because you were guaranteed a seat!! If you were the 123rd person on a 122 seat airplane, you got a plane to yourself. I am not sure how long that happened.

    2. Yes! This was an amazing proposition. I think Nicholas is right – it continued until the 1990s. I remember seeing a 727 parked outside the interim terminal, I believe. But it has certainly been discontinued.

      1. actually, they continued it until the mid 2000’s. Not only did they have spare aircraft, they had spare crews. I know someone who bid that position for many years. You sat downstairs in a crew room. Used ONLY when an additional shuttle was needed. Most of those crews sat around, reading, watching Movies, needle-point etc…..for weeks on end, without being used. Nice pay if you can get it.

        1. Wouldn’t your skills deteriorate? Actually doing your job sometimes is helpful for staying good at it.

          Didn’t somebody here say that Cape Air still does this at BOS? They’ll send as much plane as they need for whoever shows up? A bit different with their fleet, but still interesting.

          1. You’re (flying) schedule can change, monthly. The amount of time you fly as a pilot is different because of your seniority level. “Reserve” pilots are used for irregular ops, sick calls, etc. A “line holder”, a pilot with seniority has a schedule for the month. Same with Flight Attendants. Reserve for sick calls, etc. Lines of time for more senior ones.
            And, believe me, your skills are tested regularly as a pilot and on a yearly basis for a flight attendant.

  10. Cranky,

    Did the Sand Castle give you a break down of the number and type of Airbus spares on each side of the operation? Same with the 757, although would I be correct in assuming there’s one 757 spare on each side.

  11. I’d be curious if US Airways (and other carriers) now keep more spares around because aircraft rent is a much smaller percentage cost of their operation. In the old days, the model was to fly your planes as much as possible, because a plane sitting on the ground doesn’t earn any revenue. (Think America West’s now-abandoned night-time hub at Las Vegas). That’s still the case today, but idle aircraft are a much lower percentage cost. Fuel cost is so enormous that you only want to fly the planes when you can fill them with enough higher paying passengers to pay the fuel bill. For this reason, I believe US Airways (and others) flies a much more variable schedule than in the past. This means that there are more planes sitting around (spares) at most times than before. Of course, this improves reliability, which can also have a positive impact on revenue and cost.

      1. I recall once seeing about 10 DC-9’s sitting on the tarmac near the hangars right off 494 near MSP. Crazy how many of those used to be seemingly constantly “parked.” Miss seeing the DC-10’s parked out there tho. Years ago used to see L1011’s “parked” at DFW, but the airline is slipping my mind.

        Would an airline that has some old equipment that is ready for retirement put it into service if there was a MX emergency? Those old aircraft I saw at MSP surely flew to the desert since then so could they have been used for some revenue flights if called upon? Prior to going to the sand box of course.

        1. Yes. I’ve flown PHX MIA on an old Delta 757 because the original aircraft was delayed/cancelled. It was a serious POS. I’ve also been on a US Airways 757 PHX PHL because the normal A321 had a maintenance problem. Also a PHX PDX flight that turned back over northern California somewhere that then switched from A320 to 737. All of those caused musical chairs with seat assignments and some people were left off.

          1. duh, PHX ATL. Was thinking American for a second because most of their planes are POS’s anyway (in my experience).

        2. If it was an L1011 at DFW, it was probably DL. DL ran a mini-hub out of DFW until about 2003, I think. They flew quite a few TriStars out of there.

  12. Of course there are always creative ways to find a spare. I remember reading an thread where CO replaced a 757-300 with a 767-200 AND a ERJ200.

    I figure they can also bump/reroute folks if they’ve only got an A319 spare, but a A320 just went tech.

  13. Two comments. First of all, WN’s Robbing Peter to pay Paul isn’t quite what it seems. The WN network is extremely robust. This is complicated way of pointing out that in the WN system there are almost always multiple paths’s from A to B. So even if you remove the direct flight from A to B, you usually can still accomodate all of the passengers either by creatively combining flights and overflying an intermediate destination, or by simply routing the passengers one one of the many alternate routings available on the WN system.

    I also find it interesting that US uses a 757 as a spare for a 767. I guess US doesn’t operate any 767’s on long haul services, because a 767 usually has much longer legs than a 757. For example a 767-200ER is quite capable of flying upwards of 5000 miles nonstop. Good luck flying a 757 anywhere near that far non-stop.

    However since the 767 is usually considerably more generous in the seat pitch and width, there often isn’t as large a difference in seating capacity as you might expect. In the case of US Airways, the difference between a 767 and 757 can be as little as 11 seats (193 vs 204).

  14. Interesting.

    The only spare swap I ever experianced was with AA on a flight from YYZ-MIA. AA runs 3 flights a day each way and from my experiance the flights are not turn-arounds at the MIA hub and the aircrafts go on to service other flights from MIA. I was scheduled on an early am flight to MIA on the Friday before christmas break in 2010 (one of the busiest travel days of the year in YYZ). The aircraft we were scheduled to fly on was supposed to run the same flight 24 hours earlier but the flight was cancelled on a maintenance issue. According to the podium agent a repair part had just arrived. After an hour and half delay they announced repairs were not occuring any time soon and an empty plane was being ferried from ORD.

  15. After some long thinging I do recall a time when I was swapped to a “spare” aircraft. Not maintenace, but weather related. Was leaving MSP to YYC and weather at MSP had delayed the incoming aircraft. We were all told to head over to another gate and put on a supposedly “spare” A320. (This was years ago as I dont’ think any A320 is going MSP-YYC anymore.) We were all boarded and ready to go in time to make our actual scheduled departure. That was awesome. My suspicion is the CRJ’s that now fly that route wouldn’t be able to do accomodate that.

  16. Back in 2005 I experienced a maintenance swap from a 747 to a 777 on El-Al flying from Tel Aviv to London. Should have been rather straightforward, except that the landing slot at Heathrow was 747-only (I still don’t understand how this happens), so the plane flew to Stansted and everybody got to enjoy an extra 1:30 hours on the M25.

  17. The logistics get even more compounded when you consider AC swaps that require different crews. For instance, several years ago I was flying the 757/767. At that time, my company operated two flights a day to Paris: one 767 and one 777. When the 777 went down for maintenance, they swapped with a 767 which meant they had to call out a 757/767 pilot crew to fly it.

    Problem solved, right? Well, not really. When our 767 touched down in Paris, there was now a 777 crew waiting to fly it home which doesn’t work. So the company took an overnighting 767 crew in Rome who were on an extended layover and deadheaded them to Paris to fly our plane home. Then the company deadheaded us from Paris to Rome to fly that crew’s flight back to the US the next day.

    And what about the 777 crew in Paris? They got to ride back on the swapped 767.

    The bottom line is that aircraft swaps are complicated by themselves. Switch fleet types during that swap and the complications grow exponentially. And it happens every single day.

  18. Great question and answer. It would be interesting to compare a full service airline with a budget airline. I would bet the budget airline has less spares, if any. Would it also vary by route mix? For example, an airline that operates most of its routes several times be day and has an average 70% occupancy might not need spares, as it could put passengers on later flights.

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