I have a question about how very large airlines manage flight interruptions when an aircraft goes mechanical or some other mishap.

Last week a friend was flying from EWR to Tampa for business. We were both going but he needed to go a day before me.

He knows nothing about airplanes so he called me when he boarded a United 737-900. Almost the moment the crew was finishing boarding the pilot announced that the “aircraft had a mechanical problem and that it could not be fixed, so everyone would have to deplane” at the very next gate sat another 737-900 and the pilot said “we will need everyone to go over to gate XX, right next to us and board that plane” - with many apologies my friend said. My friend also said the flight was 100% full and he was afraid he’d get bumped off if the other 737 was not the same size.

Once he boarded the new plane he called to say “it’s another 737-900, I got the same seat assignment, and it has a pretty sky blue ceiling, just like the other one” - if they both had Boeing sky interiors does that indicate anything? Are they just similar in age? I left the next day on one and it looked brand spanking new! Do they have larger windows?

Anyway, my business associate left late, but arrived on time.

How did United happen to have a spare 737-900? Do they keep one or two spares at each hub? (I assume it was just a coincidence it was parked next to the broken one?) Did some other later flight lose their aircraft?

If major airlines do keep spare aircraft for emergencies like this, that must be very expensive (unless it’s a 9 times out of 10 that they WILL need it) and do they do the same for international twin aisles? (Spare 772 for example)

Normally the hubs for the network carriers will have multiple spares on site, and if there are no spares available they will start swapping aircraft until the broken one ends up as a spare later on in the day, or it is repaired and placed back into service.

Ages ago, this happened to me in MIA on a 747 going to ORD. A domestic 747...definitely a long time ago. Anyway, similar event, mechanical problem, the pilot said everyone should move over to the 747 sitting at the next gate, it would take them about 20 minutes to get it set up before we could board and we'd be on our way.

It’s not so much a spare aircraft waiting it’s having a little bit of slack in the system, case in point your business associates flight was moved to the second aircraft, the PAX from aircraft 2 will get bumped to aircraft 3 and so on until such a time that aircraft 1 is fixed and now the PAX destined for aircraft X that was the last to be bumped will now take the fixed aircraft 1

Spare aircraft cost a lot of money. The really big carriers will be able to afford them, and what will be common between large and small airlines is creative fleet management. Slack in the timetable can be leveraged, especially if they have good ground staff or handling agents who can spin an inbound plane quickly and effectively.

This gets done down a chain of aircraft until at the point where the use of slack and a spare plane covers the cancelled one. Computers help, but it's good fleet managers on the ball that are invaluable. That sick plane can then get its component shipped in or whatever has caused it to go tech, and quickly returned to traffic. Often with a big carrier it'll become the spare.

Over a decade ago I was flying SMF-IAH on Continental. When I got to the gate there was a 737-700 parked there, which was the aircraft type listed on my itinerary. Then while I was waiting and looking out the window at the ramp I saw the ground crew hook up a tug and tow our plane away somewhere. Just before boarding time they returned with a 737-300 and towed it up to our gate. We boarded as normal and everyone got their original seat assignment (I assume the layout was the same between the two types). I doubt most people even realized that it was a different plane from the one we were supposed to be on. I assume something must have been wrong with the original aircraft, but to this day I have no idea how CO happened to have a spare 737 sitting around SMF. In the pre-merger days that was a relatively small outstation for them.

VC10er wrote:

I have a question about how very large airlines manage flight interruptions when an aircraft goes mechanical or some other mishap.

Last week a friend was flying from EWR to Tampa for business. We were both going but he needed to go a day before me.

He knows nothing about airplanes so he called me when he boarded a United 737-900. Almost the moment the crew was finishing boarding the pilot announced that the “aircraft had a mechanical problem and that it could not be fixed, so everyone would have to deplane” at the very next gate sat another 737-900 and the pilot said “we will need everyone to go over to gate XX, right next to us and board that plane” - with many apologies my friend said. My friend also said the flight was 100% full and he was afraid he’d get bumped off if the other 737 was not the same size.

Once he boarded the new plane he called to say “it’s another 737-900, I got the same seat assignment, and it has a pretty sky blue ceiling, just like the other one” - if they both had Boeing sky interiors does that indicate anything? Are they just similar in age? I left the next day on one and it looked brand spanking new! Do they have larger windows?

Anyway, my business associate left late, but arrived on time.

How did United happen to have a spare 737-900? Do they keep one or two spares at each hub? (I assume it was just a coincidence it was parked next to the broken one?) Did some other later flight lose their aircraft?

If major airlines do keep spare aircraft for emergencies like this, that must be very expensive (unless it’s a 9 times out of 10 that they WILL need it) and do they do the same for international twin aisles? (Spare 772 for example)

The replacement Airplane could have been there for a later trip that could be covered by what we call a "crank-down" where we swap airplanes to open trips until the broken airplane returns to service. many times it only affects later routings or overniht work which is what we have a LARGE planning Department in Chicago for..

LX used to keep an A320 and an RJ100 on standby in Zurich, ready to be swapped in for any of the European fleet if need be. Typically, this would be different aircraft in the morning and afternoon, which would be undergoing minor maintenance that could quickly be released if need be.
For the long haul fleet, however, there were no spares, so what would happen if a widebody went tech was they'd take the A330 off the twice daily Tel Aviv rotation, replace that with the spare A320 (Tel Aviv being the only wide body destination that was within the range of the A320), and sub that 330 in for the tech widebody, and have the Gate agents bump a bunch of Y pax to the next TLV flight (and apologize to the C Pax that they were losing their flatbed seats and getting Euro business).

Had it once with Ryanair. My flight HHN-VLC had a hydraulic failure over southern France. Instead of pressing on we diverted to CRL because that's where Ryanair keeps a spare aircraft and probably a huge maintenance base, even though it was just as far as going on to VLC. Unfortunately my flight crew timed out and the relief crew took two hours to arrive.
Obviously Ryanair has it a bit easier with having spares lying around strategically throughout the network given they only operate one type.

Probably about forty years ago, my wife and son checked for EAL trip 181 - BDL to MIA. She was told that there wasn’t equipment available to operate the trip, but that they would get her to MIA. She had learned by then that her pass riders luck could be in jeopardy. In a few minutes, Mr. Hartford, the agent had the MIA passengers follow him to the BDL to BAL trips gate and load. At BAL the MIA passengers followed that agent to the BAL to MIA trips gate and load. I was checking the res system but couldn’t understand what was going on. So I called the aircraft routing folks who had me leave my number. The call back started “you’re not going to believe this, but” we just operated 181 without using using a piece of equipment. She and the kid we’re about an hour late and a half late. When I picked up my wife she said ”you’re not going to believe this” and then told me her story. And her pass riders luck continued its perfect run.

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares.
737-700, IAH
737-800, DEN
737-800, LAX
737-9ER, SFO
757-200, EWR
757-200, EWR
757-222, EWR
757-222, SFO
A320-232, SFO

The legacies typically have operational spares at their larger operations. Logistically, it won't solve every delay but it can minimize them. There's typically slack built into larger fleet types for this purpose -- for example, UA (or AA or DL) will schedule a minimal aircraft to be idle throughout most of the day at its largest hubs. Sometimes it's designated "retired" aircraft -- when DL was phasing out its 1980s/early 1990s build 757, several lived on past their official retirement to serve as operational spares -> their sole purpose was to sub for other aircraft, including smaller MD-88 etc. with standby crews.

Alternatively, they could've "stolen" the plane from another flight. It happens.

- - -

Also, recognize that subs don't have to replace identical equipment. Plenty of larger aircraft are tossed on a route just because they're available. Last fall I even flew ATL-DTW on a "retired" 763A that was filling in for an MD88...

I believe B6 still keeps a spare A-320 at LGB.

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares...A320-232, SFO

Wouldn't that A320 with the -232 code be a Delta bird? Just kidding of course...

Moe

aeromoe wrote:

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares...A320-232, SFO

Wouldn't that A320 with the -232 code be a Delta bird? Just kidding of course...

Moe

It might just be an United internal code

compensateme wrote:

Also, recognize that subs don't have to replace identical equipment. Plenty of larger aircraft are tossed on a route just because they're available. Last fall I even flew ATL-DTW on a "retired" 763A that was filling in for an MD88...

I got the opposite. Took a CRJ from DEN-COS. The 200 went tech and they swapped in a brand new 700. Very first revenue flight. They placed everyone in the very back and left the front empty which was a little odd.

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares.
737-700, IAH
737-800, DEN
737-800, LAX
737-9ER, SFO
757-200, EWR
757-200, EWR
757-222, EWR
757-222, SFO
A320-232, SFO

Wow, that's cool you have a way to source this info ! Can you share your secret for where to get this info?

On a different note, it is smart that UA is leaning on a relatively large number of 757s as spares. It can pinch hit for any narrow body and even a 767 that isn't packed to the gills. It's also a great way to keep the cycles down on a "irreplaceable" airframe, and keeping these 757s sometimes idle extends their end of life.

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares.

Another observation I am making is that UA is clever for putting three spares each at SFO and EWR, since former is prone to flow-control and the latter is prone to delays in general.

It seems reasonable that IAD does not have spares, as spares could be flown in from EWR relatively quickly. What surprises me is that there aren't any spares at its biggest hub (ORD), and not even a 737 at far flung stations (e.g. HNL or GUM) that are five to eight hours away from the nearest hub.

If a plane is sitting on a gate, chances are high it is not a spare aircraft. Gate space is extremely tight in most hubs and outstations. If a plane is not scheduled for any kind of flying and is being used as a spare, it in most cases gets moved to a hangar or remote stand. This also means that it can be extremely time consuming to bring it back to a gate if there was a need to use it. Spares also tend to be aircraft that are long term out of service aircraft or planes returning to service after a maintenance at a hangar. Thus spares are usually the last resort to use especially on narrow body fleets. It is much easier to find slack in the schedule where you have a plane scheduled for a longer sit and keeping swapping if needed until the broken plane is fixed or no longer needed for the day. Both in hubs and outstations, you do have planes that overnight to take out morning flights and often these are used to cover for an out of service aircraft to give maintenance extra time during the night to fix an out of service aircraft.

The amount of spares in a hub and system wide is often low to begin with as most planes have an assignment they are being used for. It is not uncommon for there to be no usable spares for most fleets. Usable spares can quickly early in the day be put to use as planes on routine overnight maintenance take longer to return to service than planned. Usable spares in one hub often get repositioned to another hub or station to cover flying as needed.

Just like using spares, upgrading or downgrading between variants and types of aircraft is a bit of a last resort. Moving between types and variants can mean extra time waiting for a new crew to be set up and called in and/or processing passenger oversales and seat changes in the case of a downgrade. This is one reason why having multiple seating configurations on the same type can be problematic.

Most equipment changes are move ups using planes with longer sits between flights.

brian415 wrote:

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares.

Another observation I am making is that UA is clever for putting three spares each at SFO and EWR, since former is prone to flow-control and the latter is prone to delays in general.

It seems reasonable that IAD does not have spares, as spares could be flown in from EWR relatively quickly. What surprises me is that there aren't any spares at its biggest hub (ORD), and not even a 737 at far flung stations (e.g. HNL or GUM) that are five to eight hours away from the nearest hub.

Most airlines have an ideal level of what they want to have as spares. The schedule often means that what you want versus what you have are two different things. You also need space to store aircraft that are just sitting around with no flying scheduled. Your spares are going to be in places where you have hangars and places to park them long term. I doubt UA having spares in SFO and EWR has anything to do with ATC or delays and more to do with them being hubs and maintenance bases.

In most outstations, the flying is to and from the hub. Unless it is a maintenance base, you wont see airlines putting spares at outstations even if its in a remote station. You want to have spares in a place where they can be used if needed. A spare in an outstation is very difficult to use as they could only really be used from that station and thus would sit for a long time not being used and making money. Outstations are also not usually crew bases which further limits how a spare could be used.

MSJYOP28Apilot wrote:

[..] Just like using spares, upgrading or downgrading between variants and types of aircraft is a bit of a last resort. Moving between types and variants can mean extra time waiting for a new crew to be set up and called in and/or processing passenger oversales and seat changes in the case of a downgrade. This is one reason why having multiple seating configurations on the same type can be problematic. [..]

I had an interesting experience about 15 years ago on a Saturday morning SFO-ORD flight, when UA swapped out a 767 for a A319. It was purely for economic reasons. And, presumably there were spares (of a 767 and an A319) at both hubs so that repositioning wasn't an issue. The load was like 25% and only 28-ish seats were occupied. Most passengers took a row for themselves, including me. A crew member told me that the crew were not scheduled for this flight, and he speculated that the load was too small to fly a nearly empty 767.

Bhoy wrote:

LX used to keep an A320 and an RJ100 on standby in Zurich, ready to be swapped in for any of the European fleet if need be. Typically, this would be different aircraft in the morning and afternoon, which would be undergoing minor maintenance that could quickly be released if need be.

Yes! I have heard stories from friends that work in technical operations for at least two distinct airlines that in a pinch situation, that they could pull a plane into service that was scheduled to, let's say, be diagnosed for certain "squawks". If the issue was minor, and let's say, it didn't impact safety or the MEL (minimum equipment list), they'd put the plane into service.

Interesting! The folks who figure these hiccups in logistics (someone mentioned a team in Chicago for UA) must have mega mathematical brains. I can barely rotate my laundry!
So, I get that if this happens at a big hub for an airline it would be easier to find a sub.
What happens if a large aircraft in some far away country goes tech? Example: United has only one wide body a day at GIG, if that ac goes tech at time of boarding, is another 767 or like-sized aircraft found in the USA and flown to Rio to bring those passengers home? Or, will they try and get all those passengers home by putting them on other airlines?
I had this happen many years ago and I was in J on UA. Our 767 went mechanical and VARIG took as many passengers as they could and they put me in VARIG 747 in First Class. This was over 25 years ago and I was bowled over by the service on RG that I refused to sleep and stayed up to enjoy the ride. United lost me for a while and I started booking RG to Brazil whenever I could.
But RG could only take about 20 peeps, so I heard before I boarded VARIG that United was going to fly down an empty 767 to pick everyone up...they just had to wait for a 767 to make a 9 hour flight.

In 2014, the 763 (N178DN) which was scheduled for my DL flight from JFK to FRA went tech. About an hour later another DL 763 (N182DN) showed up at the next gate from MSP. It had some passengers and I guess it was a repositioning flight after some maintenance at MSP. It was probably scheduled for a flight the next day, but instead became our ride to FRA that night. We were only delayed a little more than two hours.

KVH68 wrote:

aeromoe wrote:

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares...A320-232, SFO

Wouldn't that A320 with the -232 code be a Delta bird? Just kidding of course...

Moe

It might just be an United internal code

That's the code for IAE engined A320 series for your reference.

Michael

Airlines maintain operational spares...usually at a hub, but sometimes at a centrally located station where it can fly to a mechanical.
Back in the day, both UPS and FedEx flew operational spares during their launch window in order to better recover from a mechanical problem.

compensateme wrote:

Also, recognize that subs don't have to replace identical equipment. Plenty of larger aircraft are tossed on a route just because they're available. Last fall I even flew ATL-DTW on a "retired" 763A that was filling in for an MD88...

And sometimes it goes the opposite way.. I remember reading somewhere (perhaps here?) that CO had a 757-300 that went tech, and they replaced it with two flights, one was a 767-200 operated by CO, the other was a CRJ200 operated by ExpressJet. (Yeah, the 757-300 had more seats than the 767-200.)

VC10er wrote:

Once he boarded the new plane he called to say “it’s another 737-900, I got the same seat assignment, and it has a pretty sky blue ceiling, just like the other one” - if they both had Boeing sky interiors does that indicate anything?

It indicates they were 2011 or newer 900ER's.

VC10er wrote:

Are they just similar in age?

Somewhere within six years of each other.

VC10er wrote:

I left the next day on one and it looked brand spanking new! Do they have larger windows?

No, the windows are the same size.

brian415 wrote:

KVH68 wrote:

There are very few spare aircraft around the United system. At this exact moment in time, there are 9 spares.

Another observation I am making is that UA is clever for putting three spares each at SFO and EWR, since former is prone to flow-control and the latter is prone to delays in general.

It seems reasonable that IAD does not have spares, as spares could be flown in from EWR relatively quickly. What surprises me is that there aren't any spares at its biggest hub (ORD), and not even a 737 at far flung stations (e.g. HNL or GUM) that are five to eight hours away from the nearest hub.

The spare at ORD might have already been used to substitute for an out of service airplane. The information I gave is just the spares at that exact moment. This list will fluctuate during the days as aircrafts are used and others put into the spare list.

I can't imagine a spare would be sitting at a gate. If they have a maint facility that makes sense they would have spares. I can name a few times that they didn't have spares waiting. I'm going MEM-ORD-LHR and the United regional has a water leak in the galley. they turn back and end of flight. I fly 2 weeks later. My daughter was flying SFO-ORD on United. There's a mechanical on the jet way before boarding time. They make the pax wait until they can use another jet coming from HOU. Major delay.

The folks on this EDI-LHR shuttle service back in 1994 must have got a shock at the change of aircraft.

https://www.youtube.com/watch?v=gR083lAK9jk

(scheduled) ground times and flights don't always match up. so even with the most efficient flight schedule the ground time of an aircraft mitght be an hour more between flights than needed. so maybe the other aircraft was to depart an hour after the original flight, so they switched. this extra hour might be enough to fix the issue or maybe even another aircraft jumped in. or the flight this "spare" aircraft was originally planned for gets delayd for maybe half an hour (which is better than delaying the original flight for one and a half hours).
aircraft even get swapped to get half an hour extra. this might make the cut to get the flight out on time or shave off of the delay.

usually airlines don't have aircraft just sitting around all day "just in case". they are most probably aircraft that would be needed later but have some time extra that is "transferred" to the other flight

VC10er wrote:

Interesting! The folks who figure these hiccups in logistics (someone mentioned a team in Chicago for UA) must have mega mathematical brains. I can barely rotate my laundry!
So, I get that if this happens at a big hub for an airline it would be easier to find a sub.
What happens if a large aircraft in some far away country goes tech? Example: United has only one wide body a day at GIG, if that ac goes tech at time of boarding, is another 767 or like-sized aircraft found in the USA and flown to Rio to bring those passengers home? Or, will they try and get all those passengers home by putting them on other airlines?
I had this happen many years ago and I was in J on UA. Our 767 went mechanical and VARIG took as many passengers as they could and they put me in VARIG 747 in First Class. This was over 25 years ago and I was bowled over by the service on RG that I refused to sleep and stayed up to enjoy the ride. United lost me for a while and I started booking RG to Brazil whenever I could.
But RG could only take about 20 peeps, so I heard before I boarded VARIG that United was going to fly down an empty 767 to pick everyone up...they just had to wait for a 767 to make a 9 hour flight.

If you are not at a hub, focus city or major maintenance base, you are basically hosed if the plane brakes at departure time. The only possible equipment swap is usually to wait for the next inbound overnighting plane of the same type and hope the crew is still legal to wait that long. Rescue missions are not very common and may not be possible unless the airline wants to cancel another pair of flights to free up the equipment and crew to do so. Re-booking or simply waiting for the plane to be fixed are really the only options. Because planes are needed back at the hubs, a revenue flight is still often operated to get the plane back to the hub even if the plane has to sit for a few days to get fixed at the outstation. If a plane will be a day or more delayed, it is not uncommon to cancel the original leg and operate it with a different flight number as an extra section when the plane does return to service.

Its called rolling the fleet.
If you have a/c that are not always on minimum turns when you end up with a U/S A/C you replace that with the next and keep going until the U/S one can be put back into the pack. It saves the cost of spare A/C but does mean you utilise the aircraft less.

eamondzhang wrote:

KVH68 wrote:

aeromoe wrote:

Wouldn't that A320 with the -232 code be a Delta bird? Just kidding of course...

Moe

It might just be an United internal code

That's the code for IAE engined A320 series for your reference.

Michael

To all, my post was a joke (probably to me only), referencing DL's Boeing code as "32" and the fact the A320, with the engine you specify, is also a "32." I've been spotting planes for more than 40 years...a helluva lot longer than many of the A-netters have been alive...a little humor is bound to occur occasionally...even if its funny only to myself.