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I've spent far too long staring at flight tracking sites, and occasionally I think I'll notice some pattern in what types of aircraft a given airline uses for certain scenarios/routes.

For example, Delta seems to operate a lot of MD-88's on short-haul routes that other airlines would likely use ERJs or CRJs on. They also seem to use 757s on quite short hops (ATL to southeastern cities ~1hr away).

Another example would be why British Airways operates 747s to some cities, and 777s to others, and exactly how they decide where to use which aircraft.

Is there a good reference for figuring out the reasoning behind why airlines use a given aircraft for a given route? Or are there too many different factors and too much corporate secrecy to really know for sure?

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    $\begingroup$ Without sending them an email and asking I presume? $\endgroup$ – ratchet freak Nov 28 '18 at 14:51
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    $\begingroup$ It all comes down to economics. If Passenger income is > Plane cost (long term leases) + fuel cost + crew cost + meals costs + terminal fees + ground crew fees + overflight fees + overhaul/inspections + indirect costs ... then the flight is making money. If not, then one way to make a profit is to change the plane & payload. Or, eat the loss and make it up on other routes to keep the lossy route open, say to feed the larger planes flying from a hub for long distances from smaller out of the way airports. I'm sure a large corporation like BA has this all modelled and tracked very well. $\endgroup$ – CrossRoads Nov 28 '18 at 15:49
  • $\begingroup$ @ratchetfreak I mean, that is a very logical option I hadn't considered. Definitely worth a shot! $\endgroup$ – zymhan Nov 28 '18 at 16:19
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    $\begingroup$ An airline I once worked for regularly flew half empz767s on a route otherwise operated by a narrowbody because the extra underbelly cargo paid for it all. So no, often it’s not obvious... $\endgroup$ – Cpt Reynolds Nov 28 '18 at 16:51
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    $\begingroup$ @CptReynolds I dream of finding a ticket on one of those flights where the plane is far larger than it need to be (with respect to just passengers). I've noticed 777s flying DTW-ATL, and I can't imagine those are very full. $\endgroup$ – zymhan Nov 28 '18 at 18:53
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There are many factors, but you can often predict what class of plane will be used for a particular route by the distance and demand.

For smaller cities, they want to fill the planes, but they also need several flights per day to cover the fixed costs of serving that airport (and make things convenient for customers), so it's often better to have a commuter jet bouncing to the nearest hub and back several times per day day than one large plane that carries an entire day's worth of passengers in one shot. For larger non-hub cities, they'll do roughly the same thing but with mid-size planes.

Between hubs, they'll run the largest narrow-bodies to connect all the various small cities not served by a common hubs, plus hubs themselves tend to be large cities with plenty of native demand too.

For international, they'll run wide-bodies because they need higher fuel capacity, and there's rarely a convenient time for customers due to the long flight times combined with crossing several time zones, so you might as well pack them into as few planes as possible.

Notably, some carriers fly several different types, each optimized for specific route types, while others fly just a few types (or even just one) because that makes maintenance, pilot training and fleet scheduling easier--but may limit what kinds of routes they can fly profitably. When airlines merge, they'll usually have similar fleets--and in cases where they don't, they'll quickly start dumping types they don't like and replacing them with types they do.

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Every airline has their own recipe and priorities in this regard and it’s unlikely you will find any open accessible references to this.

Apart from the obvious demand, availability and costs of aircraft and business they do take in consideration the wear and tear (and maintenance cycles) of the aircraft (how long to go before what maintenance) as well as a balance of long and short haul operations and the specifics of each particular aircraft and its parts. An aircraft with some inoperative equipment might still be legal and dispatched for a short haul flight but not ETOPs operations.

It can go down to small details like customer profile and preferences as well as configuration of the aircrafts interior (eg. newly upgraded seats) and the availability of service and maintenance facilities.

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    $\begingroup$ That makes sense. Is aircraft maintenance related to hours, or cycles, or both? I imagine if some parts are cycle-bound, and some are hour-bound, that you might end up with a mismatch over time, where the craft has flown relatively few longer-distance flights, or vice versa. $\endgroup$ – zymhan Nov 28 '18 at 18:59
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    $\begingroup$ Depending on the items it could be: calendar time, landings, operating cycles, flight hours or block times. Some parts are checked on condition maintenance which is a periodic inspection or testing of the components or structures against a known standard or wear limit. $\endgroup$ – mbglobetrotter Nov 28 '18 at 19:24
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    $\begingroup$ A major German carrier used to fly 747s on German domestic routes (for reference, if required - it’s hard to squeeze more than 600NM into a German domestic route) at one point before their retirement, allegedly because the airframes were coming up to their next scheduled base maintenance input on hours, but not yet on cycles. $\endgroup$ – Cpt Reynolds Nov 28 '18 at 21:46
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You also get the occasional really big planes on routes that wouldn't seem to necessarily make sense for the distance. This can happen when there's a big out and back that brings the plane back to the hub with some "downtime". For example, out of SFO, a large plane may fly a 8 hour leg out to a far point, and then come back. Adding time in for servicing etc, the plane would arrive back at the hub site around 18 hours after it left. It could serve the same route and just sit on the ground for 6 hours waiting, but why not send it back and forth to DEN for example, which it could do in that downtime. Or maybe the timing works to have the plane go to the east coast and then do a long trip out of there.

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    $\begingroup$ This makes sense! I've noticed much larger than normal flights operating between two international hubs, presumably because it was needed for an international flight from the destination city. $\endgroup$ – zymhan Nov 28 '18 at 18:56
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    $\begingroup$ You can find this kind of stuff out on flightaware using the "track inbound plane" function. I just started playing with UA340 which is a 777 IAD -> SFO and just keep hitting 'track inbound' to see where this tail number has been. Back far enough we get HKG -> ORD : ORD -> EWR : EWR -> FRA : FRA -> ORD :ORD -> FRA : FRA -> IAD :IAD -> SFO and presumably SFO to a long haul destination. $\endgroup$ – Aaron Nov 28 '18 at 19:03
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    $\begingroup$ Maintenance is also a factor here: the airline may route aircraft to a particular hub where they have maintenance facilities. If a UA 777 ends up in IAD and is due for maintenance at the base in SFO, they can either use it for a revenue flight or ferry it empty, so why not try to fill it up? $\endgroup$ – Zach Lipton Nov 29 '18 at 6:55
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    $\begingroup$ Another reason for this: ETOPS is not allowed for the first flight after maintenance, so a large twin may need to fly one domestic flight before it's legal to return to international service. $\endgroup$ – StephenS Dec 1 '18 at 20:06
  • $\begingroup$ @StephenS I'd never heard that rule before! $\endgroup$ – zymhan May 21 at 12:58

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