I was wondering what aircraft maintenance entails, how long it takes, how frequent it is, etc. I've heard there are A checks, B checks, etc. but I would like to know what those are and how frequent they are. Maybe if it varies by aircraft use the A320 as an example. Thanks!

Also wondering whether airlines carry out maintenance themselves or contracts it out?

There are a few maintenance checks

• Daily Checks/Pre Departure Checks/ETOPS. Done at least every 48 hours for narrowbodies and every flight for widebodies. Takes about 15mim-60min. This consists of tire pressure, Brake wear, engine oil, looking for status messages, clearing the logbook and addressing deferred maintenance.
• Weekly checks (every 7-30 days depending on type of plane) where deferrals such as cabin items are worked, navigation databases are updated, recurring structural inspections are done, gear struts are checked, Hydraulic fluid topped off, tires and brakes are replaced when near limits, etc
• A Checks, typically every 3 months and about 750-1000 flight hours. Here some task card inspections are done. Landing gear, flaps and flight controls are lubricated. Doors are checked and cleaned. General visual inspection of the plane. Ranges from 8 hours to 48 hours long.
• B Checks. Not all airlines do B checks. They are essentially are more intensive A check that lasts a few days. These are every 6-12 months.
• C Checks, every 2 years and about 6,000-10,000 flight hours. Lasts 5-30 days. Airplane is thoroughly inspected. Seats are removed. Interior cleaned. Many panels are removed. Landing gear may be checked. Lots of systems checks of backup redundant systems. Lots of structural inspections and repairs. Service Bulletin work is done and AD mandated inspections are often done
• D Check. Every 8 years. Typically only done on the bigger widebodies like 747s and 777s. 30-60 day’s long. Airplane gets overhauled. Landing gear is replaced.

PHXWRLD wrote:

I was wondering what aircraft maintenance entails, how long it takes, how frequent it is, etc. I've heard there are A checks, B checks, etc. but I would like to know what those are and how frequent they are. Maybe if it varies by aircraft use the A320 as an example. Thanks!

I worked for United and Maintenance o some sort is carried out Daily. A#1 svc is done every day and is basically a walkaround looking for Obvious defects, Leaks etc.
A#2 svc is accomplished when the aircraft is on the ground for more than 4:45 and consists of basic servicing and checks of tires, Brakes, fluids and "gasses" Nitrogen and Oxygen. Lights and any pilot writeups or scheduled Items. An A check is a segmented check that includes the #1 svc the #2 svc and other checks for specific items including and time controlled items, and a lot of cabin checks and repairs as needed. The C check is a minor overhaul done on either time or calendar basis and the HMV is an overhaul with time change items and encompasses a complete removal of the interior and could also have landing gear changes in the package. All the systems are thoroughly checked and the Airframe is thoroughly inspected and repaired if necessary. Not many airlines still use the B check anymore, the D check and the Heavy Maintenance visit (HMV) are the same thing. Other things and special inspections are accomplished by Engineering Orders, and are or could be Recurring checks. AD Notes, Service Bulletins or any of the above. Engines are on Condition so as long as they're generating Power? They are not usually removed unless there is wing or Pylon work that requires their removal. An HMV could also entail the vertical stabilizer removal if necessary.

Are hangers needed for A checks?

Why do they only do D Checks on WB?.

PHXWRLD wrote:

Are hangers needed for A checks?

Usually not Required. Depending on where in the world the plane is, some A checks are done in hangars. Widebodies are more likely to be done in hangars. There are wind limits that can prevent working on lifts. Also it’s tough on ground crews to work outside in winter. Some structural repairs and lubrications can’t be done in extreme cold, heat, wind or rain. Hangars are more efficient for getting work done faster, but cost money. For example You might have two simultaneous A checks And two C checks going on and only one hangar spot. The supervisors lookS at workload for each plane when deciding what plane gets to use The hangar.

C Checks are almost always done in hangars for at least part of the check. Many structural items require precise measurements and repairs that can’t be done outside.

Ok, I’m going to go ahead and throw this out there, every operator will have a different maintenance program that is developed using manufacturers’ guidance, and approved by the regulator.

What is true for United, may not be true for American, may not be true for Southwest, may not be true for UPS, may not be true for Allegiant, is almost certain not true for British Airways or Lufthansa.

Maintenance programs are operator specific.

bennett123 wrote:

Why do they only do D Checks on WB?.

Narrowbodies have simpler maintenance programs with much simpler structural inspections. Opening up panels for inspections is easier on a narrowbody. They usually are designed around a series of C Checks with varying scope of work in each check. MSG-3 analysis allows maintenance tasks to be scheduled based on some analytical failure analysis methodology.

https://www.aviationpros.com/engines-co ... aintenance

For example the 747 maintenance program was developed before MSG-3 when maintenance schedules were not done using Weibull analysis for reliability centered maintenance program. That program was built with both C and D checks. The 747 is one of the only planes still being build designed around having D Checks. Other airplanes can have them, but airlines tend to fit that work in the c checks instead all at once in a giant D check

bennett123 wrote:

Why do they only do D Checks on WB?.

To me previous post, we don’t do D Checks. All our D Check tasks, such as they are, are segmented out and performed during C Checks.

fr8mech has the biggest point, all operators have different programs with different names for all of the different level of checks. What is included in one carriers 'A'/Service Check may not be in another operators. Plus they are always evolving. I've been out of hangar /line mtc for about 5 years now. I'm sure what is on the different checks is someone changed.

We never lubed much during A checks. Major lube tasks were done on a stand alone visit. Usually one for flight controls and another for gear. Narrow body gear usually just got added to a overnight "daily check" and were done where ever the plane was parked. Most of our flight control lubes were done in a hangar mostly due to that's where we had the most access to man lifts quickly. For a 757 lube we would use 1 basket lift (not me!) for the vertical, 1 electric man lift for the horizontal, 2 electrics for the flaps(2 AMT's each), and 1 more for the slats since they got lube on alternate visits per side. One other AMT would do the daily stuff. That was one 10 hour shift overnight.

Our A checks were single overnights also. Most of the time they were done where ever the plane was parked. Oil and fuel filters, hydraulic filters. A list of flight control ops checks and other system checks. The tasks varied by fleet types and where in the rotating cycle of checks that plane was. Usually 2-5 AMTs for one shift.

Our C checks typically ran 2-3 weeks. There is a lot of optional work that gets loaded into these checks. I would guess half of the work is optional. Performance or reliability driven upgrades. Or marketing driven like interior minor changes. The big killer is the focused structural inspections. Inspectors had tasks to look at know bad areas for corrosion or fatigue cracking. Sometimes nothing was found. Other times it was remove the galley and do floor beam repairs or other very time consuming work. These checks were every 2 years. A series of 4 checks that alternated heavy and light with the last being the full crown inspection that required cabin strip. That one at DL has been an out source check for a while now. It required a lot of man hours.

PHXWRLD wrote:

Are hangers needed for A checks?

Not really.. If the weather is good? then an A check can be accomplished on a Gate with 2-3 mechanics in 6-8 elapsed hours. Unless you have to change all the tires and Brakes for being worn out. Which in my 10 years working the terminal on Mids? I've never had to do. Matter of fact? I've never had to change more than 2 brakes at any time except once on a 747. But? Since there were 16 of them? I just lucked out as they were both on the AFT body gear positions and at the time? We were using lightweight Non re-capable tires in the 49x17 size (Goodyear Flight Eagles) On the 747 they aft body gear tires take more abuse than any other tire because they're
the first to Hit the ground and the last ones to leave the ground.

Dalmd88 wrote:

fr8mech has the biggest point, all operators have different programs with different names for all of the different level of checks. What is included in one carriers 'A'/Service Check may not be in another operators. Plus they are always evolving. I've been out of hangar /line mtc for about 5 years now. I'm sure what is on the different checks is someone changed.

We never lubed much during A checks. Major lube tasks were done on a stand alone visit. Usually one for flight controls and another for gear. Narrow body gear usually just got added to a overnight "daily check" and were done where ever the plane was parked. Most of our flight control lubes were done in a hangar mostly due to that's where we had the most access to man lifts quickly. For a 757 lube we would use 1 basket lift (not me!) for the vertical, 1 electric man lift for the horizontal, 2 electrics for the flaps(2 AMT's each), and 1 more for the slats since they got lube on alternate visits per side. One other AMT would do the daily stuff. That was one 10 hour shift overnight.

Our A checks were single overnights also. Most of the time they were done where ever the plane was parked. Oil and fuel filters, hydraulic filters. A list of flight control ops checks and other system checks. The tasks varied by fleet types and where in the rotating cycle of checks that plane was. Usually 2-5 AMTs for one shift.

Our C checks typically ran 2-3 weeks. There is a lot of optional work that gets loaded into these checks. I would guess half of the work is optional. Performance or reliability driven upgrades. Or marketing driven like interior minor changes. The big killer is the focused structural inspections. Inspectors had tasks to look at know bad areas for corrosion or fatigue cracking. Sometimes nothing was found. Other times it was remove the galley and do floor beam repairs or other very time consuming work. These checks were every 2 years. A series of 4 checks that alternated heavy and light with the last being the full crown inspection that required cabin strip. That one at DL has been an out source check for a while now. It required a lot of man hours.

At United? We did minor lubes during our A checks but we had a K check that was nothing BUT a lube and it took 2 guys most of the night to do as a line check.
During C Checks ? They lubed the entire aircraft and it was an 8 man crew that did it. And LORD they were good!

When I went back to Hangar from Line guys hated me. I would have a wing tailing edge done in a couple of hours. The other side planned on a whole day. For me it was super easy to be working off a wing stand instead of moving an electric highjacker around. After a few months I rarely did lube cards anymore. I was either doing sheetmetal liek int he old overhaul days, on an engine or filling a spot with hydraulics. Some days I would even sub into the Avionics crew when they needed an extra hand. That was weird at first. They didn't believe a mere mortal AMT could read a wiring diagram, run wires, and crimp pins.

Candid question : what are the differences in terms of process between a jet like E190 for instance and a Turboprop Dash 8 - Q400 ?

A380MSN004 wrote:

Candid question : what are the differences in terms of process between a jet like E190 for instance and a Turboprop Dash 8 - Q400 ?

Not much difference I would imagine. It might depend on the regulatory status the plane is operated under, say 121 vs 135. From my standpoint they don't have much difference. Both a small jet aircraft. Yes, one has a prop and the other has a big fan. Really they are very similar. Small vs large just more airplane. The E190 might have better avionics, but it wouldn't change the required inspections and servicing tasks.

Dalmd88 wrote:

A380MSN004 wrote:

Candid question : what are the differences in terms of process between a jet like E190 for instance and a Turboprop Dash 8 - Q400 ?

Not much difference I would imagine. It might depend on the regulatory status the plane is operated under, say 121 vs 135. From my standpoint they don't have much difference. Both a small jet aircraft. Yes, one has a prop and the other has a big fan. Really they are very similar. Small vs large just more airplane. The E190 might have better avionics, but it wouldn't change the required inspections and servicing tasks.

Most people don't realize the DHC-7 was one of the first CAT-3 airplanes ever built. and was one of the first airplanes to ever shoot an approach using the Microwave landing system. I don't think any airline other than Time Air ever got beyond a CAT3A capability and most could shoot an approach down to 100' and 1/2 Mi visibility.
While flying in USN P3 service we had to shoot a 0/0 landing as we were running out of fuel to not land after having stayed on station for 15.5 hours chasing a Soviet Alpha boat harassing the Big E in the southern Atlantic. Which was the ONLY time I ever flew with an "Alpha" Loaded airplane carrying Live MK-46 Torpedoes and B-57 Nuclear Depth charge. I flew other warload flights like when Khadafi threatened the 6th fleet. but I knew we would whip his ass before we even got out on station so I felt pretty sure we were coming back with the load we took out. I was deployed to NAS Bermuda.

Avionics are always an option for the operator. I worked on a Metro that had everything. MLS, GPS, Inertial Nav and even Omega. It also had a bunch of real nice cameras mounted in a pod under the belly. That was back in 1996.

JayinKitsap wrote:

Quite interesting info - thanks



So a 757 lube is about 60 manhours? Is the 737 easier? Is the lube at 1 month intervals?

On the structural checks how is it tracked what portions inspected if not the whole plane? Are there defined areas that are always done in full or is it logged by diagram in the reports? I've had to track weld inspections on construction sites and it can get complicated really fast to ensure all are checked, if in doubt it was done, it gets done again.

Does the day shift work the larger jobs with a plane having 2 mechanic shifts a day or is the night shift only working the overnight jobs.

For our operation the 757 and the 737 packages are different. I only recall doing the trailing edge lube tasks wile working Line Mtc. It was way simpler task on the 737. Almost no panels to remove and about half as much flap mechanism. It was typically a one man job tacked on to the regular overnight tasks. I don't know the intervals, planners put into the work package when it is coming due. More than a month though.

Tracking for the structural inspections is built into the total plan of the cycle of all the C check inspections. I think the 737 had like 8 or 10 different C checks. So if the overall plan said an area need to be looked at every 4 years XXXX cycles it would be on every even numbered C check. If it was more frequent it would be on every check and possibly added to some of the A checks. This is all stuff done by Mtc Planning.

Dayshift at Line stations typically doesn't do any big jobs. The planes are flying. The exception is some international ops stations would likely do A checks while the plane sits all day. Otherwise they are Firemen. Sit and wait for something to go wrong. They will go out meet planes between flights, do a quick unoffical walk around checking tire condition, checking engine oils. A plane might get flagged for a official light thru flight check if it has not overnighted at Mtc station resently.

Second shift does the same, but usually starts doing some of the overnight checks from the early terminate planes. My old station had around 15 overnights every night. Seconds would get the first 2-3 done before they left.

Third shift for Domestic Line is where the bigger staffed crews are. Out of those 15 planes we typically had one heavy plane with an A check or 757/767 lube. The rest would be regular 1-2 man airplanes with an overnight check and some other tasks, plus work on all the broken stuff.

For our C check hangar work, we tended to have a larger Day shift and smaller second and midnights. They could have been even numbers, but it was an attempt to make life easier for more mechanics.