[AVIORADAR VISITED] Croatia Airlines line maintenance


With the goal of educating our readers on all segments of the flight, we’ve visited Croatia Airlines’ technical services and their sector for line maintenance.

Aircraft maintenance in every MRO (Maintenance and repair organisation) is divided in two branches – base and line maintenance, and Croatia Airlines is no different.

Line maintenance is covering all minor scheduled and non-scheduled work, performed in a way that doesn’t interfere with the aircraft’s flight schedule. Checks that are performed within the frame of line maintenance are mostly related to preventive checks. They include:

Daily check which is performed after last flight of the day. Its purpose is to check the aircraft from any damage and to check its overall performance. In order to perform these checks, special tools are used to verify whether the aircraft can maintain its flying certificate. Some of the checks are: visual inspection of the fuselage, fluid check (engine oil, hydraulic fluid, etc.), and emergency equipment checks.

Weekly check includes replacement of the engine oil and any other liquids onboard the aircraft, such as hydraulic fluid, engine starter oil, etc. Aircraft fuselage is visually inspected, as well as landing gear and engines. Exterior lights are also inspected and checked. If necessary, tires on landing gear are replaced.

Transit check is performed between two flights, and it includes visual inspection, scheduled works and repairs of any possible damage.

 Before we were headed to the apron to spend a part of the day with line maintenance mechanics, we had a word with the manager of Croatia Airlines line maintenance, mr. Roberto Šanić. He explained all the functions and tasks of line maintenance to us.


Could you explain to us how Croatia Airlines’ line maintenance works?

Line maintenance in all companies, as well as in Croatia Airlines, works more or less the same, and has to be that way because everything is regulated. Our works are part of EASA Part 145 regulation (approval for MRO for aircraft maintenance). Aircraft maintenance is carried by the order of our client, and in compliance with regulations. In our case, our primary client is Croatia Airlines, but we also cooperate with other carriers, such as Qatar Airways, British Airways, etc.

Basically, line maintenance is in charge of the ongoing traffic, and they are dealing with everyday problems on daily basis. Minor malfunctions are repaired, we are preparing aircraft for its next flight or for the first flight of the day.

Croatia Airlines, apart from Zagreb, also provides line maintenance services in Split, Dubrovnik, Pula, Sarajevo and Skopje.


What are the standard tasks on the aircraft within the frame of line maintenance?

These are works that are part of daily, weekly or transit checks. Some carriers even cary out F checks (first check of the day) through line maintenance, but that’s not obligatory since the crew can open the aircraft and check everything before first flight. Line maintenance covers all checks to A check – first big check on the aircraft.


What is included in daily and weekly checks?

Daily check includes performing of scheduled tasks, fixing any defects and preparing airplane for flight. Weekly check includes additional and more detailed checks of fluids, check of all seats, etc. Overall, weekly check is a bit more detailed than daily.

Which are the standard tasks for line maintenance?


Those would be check and replacement of tires, adding oil to the engine and engine starter, adding hydraulic fluid etc.


How does line maintenance function in terms of aircraft scheduling?

We have contracts with some companies that obligate us to regularly go to the aircraft, no matter if there are any malfunctions or not. With other companies we function upon a call. Crew calls us if they are having any problems with the aircraft.


On which types of aircraft can Croatia Airlines do maintenance?

Again, Croatia Airlines is working according to EASA Part 145, and we can work on the aircraft that we have in our scope. Generally speaking, we can maintain Airbus A320 family of aircraft (A318, A319, A320, A321) with both CFM and V2500 engines, ATR 42/72, Dash Q400, CRJ 900 and CRJ1000. Soon we will add new aircraft to our scope, Airbus A320neo family, also with both engines, Pratt & Whitney and CFM Leap.


What happens when an aircraft in need of repair comes to Zagreb Airport, and that type of aircraft is not in your scope?

By the regulations, there is something called ‘one off approval’. For example, we have one maintenance engineer that has licence for Airbus A330, although we don’t have A330 in our scope. In that case, airline carrier can issue ‘one off approval’ for this mechanic to do specific work on the aircraft.


How often are the aircraft late due to complicated maintenance works?

This happens very rarely. The idea od line maintenance is not to mess the flight schedule, so all works are planned according to that.


So passengers should not meet with one of your mechanics and engineers?

No, there is no need for that. All scheduled work is performed while the aircraft is empty. The cases in which passengers can see our mechanics are very rare, mostly when they are dealing with some minor repairs. Passengers can often see our mechanics when they are consulting with the crew about current condition of the aircraft.

Lastly, I would like to point out that safety is our number one priority, there are absolutely no compromise made here. Safety is always first and above all. Regarding our business plans, our goal is to offer as many aircraft in our scope as possible, and to define ourselves as a regional leader in providing aircraft maintenance works.


We wanted to see closely what it is like to work as a line maintenance engineer, and that’s why we spent our day with them on their terrain – apron of Zagreb Franjo Tuđman Airport.

What seemed to us like a chaos, it’s actually a perfectly organised system. Team of mechanics are positioned on all sides of the apron, each with his task and his aircraft. During our visit, there were no repairs, only regular tasks such as opening of the aircraft, starting up the aircraft and APU, dealing with the paperwork from previous work etc.

The daytime shift starts with a morning inspection of the plane, with so-called  F check. F check is a check performed before the first flight of the day. It consists of an inspection of the exterior of the aircraft, walk-around to examine the exterior, tire pressure, engines, etc.


After checking the exterior of the aircraft, the mechanic goes to the cockpit to turn the aircraft systems on, in order to prepare the aircraft for the arrival of crew. This procedure consists of powering the aircraft’s electrical systems, adjusting the navigation devices – aligning the navigation system, preparing tablets for the Captain and First Officer, radios are switched-on, fuel quantity selected, and if necessary, they heat or cool the aircraft cabin to make it especially comfortable for the passengers when they embark the airplane.


While Croatia Airlines flights are departing Zagreb for their morning flights, Qatar Airways  flight lands in Zagreb, usually with the Airbus A320 type of aircraft. A technician makes a Transit Assistance on it, fixing possible issues on both aircraft systems and in passenger cabin and refuels the aircraft. After that, he fills in the TLB – Technical logbook and sends the aircraft back to Doha.


The work day is continued with day-to-day support for British Airways aircraft, consisting of aircraft refueling and handling the required paperwork, which is then delivered to the flight deck crew for inspection and signature.

In the afternoon, technicians are waiting for arrival flights to Zagreb and are always on standby if the crew has some issues on one of their aircraft. One of the technicians is waiting for another Qatar Airways flight, where he performs the transit inspection and refueling.

On Tuesdays, Thursdays, Saturdays, and Fridays only during September, the line maintenance of Croatia Airlines is assisting on Airbus A330 of Korean Air. During the winter flight schedule, Korean Air flies to Zagreb with the new type of Boeing 787 Dreamliner, where Korean Air technician does the walk-around, and Croatia Airlines tehnician helps during the pushback and fixes all the defects on the aircraft, of course if there are any.


If required, technicians also go to the aircraft of the companies other than the aforementioned British Airways and Qatar Airways, who request assistance for any reason. Some of the other companies using the services of Croatia Airlines Line maintenance are: Aeroflot, Iberia, Brussels, Lufthansa etc. It is called ”On-call support”


During the night shifts all (larger) planned and unplanned work is carried out. The planned work include: visual checks of the oil chip detectors in the oil system, tests of various electrical systems on the aircraft, weekly checks, aircraft engines oil checks, engine exchange due to the expiration of the resources which need to be send to overhaul… The unplanned work usually consists of changing the tires, bulbs etc. After all the work is carried out, the aircraft is closed, sealed and prepared for the upcoming flights.


In the end, we can conclude that the line maintenance has a very important role in the whole process of flight planning. Safety of the passengers and crew is an absolute priority, above everything else. Therefore, we as passengers, should understand that our flight is sometimes late because people in charge of our safety are doing final checks of the aircraft, making sure our safety is not compromised in any way.

We would like to take this opportunity to thank Croatia Airlines and its Technical services sector for giving us the opportunity to write this report. We would especially like to thank Mr. Roberto Šarinić, chief of line maintenance, as well as the team of line maintenance mechanics: Karlo Mudri, Tihomir Markuš, Mario Župetić, Dinko Lucin and Karlo Horvat for their excellent hospitality.



YOUR FLIGHT: Behind the Scenes


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 Foto © Avioradar (8.7.2019 – LDZA)