Every C-130 mission begins on the ground. Behind the high-stakes airlifts, cargo drops and special missions, there are teams of technicians and engineers making sure these aircraft will perform under pressure whenever they’re needed.
It’s not a small job, as Marshall’s Chris Romanowski can attest. Chris and his team handle all of Marshall’s maintenance, repair and overhaul (MRO) work for the United States Marine Corps (USMC), which operates the world’s largest fleet of KC-130J tanker aircraft.
Few people are better-placed than Chris to explain exactly how Marshall keeps aircraft mission-ready and mission capable for customers around the world.
In a new video, Chris shares a behind-the-scenes look at the work taking place in Marshall’s hangars. He provides a detailed walkthrough of the C-130 servicing process, from paint strip all the way to final flight test and delivery—including some of the key challenges encountered at every stage.
Welcome to 16 Hangar
The footage featured in this video was almost exclusively shot in 16 Hangar, which is Marshall’s dedicated facility for USMC maintenance.
The hangar itself comprises four MRO bays out of a total of 14 across Marshall’s site in Cambridge, UK. In addition to 16 Hangar, one slot in an adjacent hangar was recently made available for USMC work due to the high volume of inputs.
Since 2020, Chris and the USMC team have worked on more than 50 inputs and racked up at least 350,000 hours of work for this customer alone. After five years on contract, many of the incoming aircraft are no longer first-timers at Marshall, having been serviced here at least once before.
Know your MDIs from your PMIs
As Chris explains, Marshall performs two main types of servicing on USMC aircraft: minor depot inspections (MDIs) and planned maintenance intervals (PMIs).
An MDI is a quick routine inspection—roughly equivalent to a “B check” in more general aviation maintenance terminology. These tend to take place at 540 day intervals, with the aim of bridging the gap until heavier maintenance. Paint and most components stay on the aircraft, and the team ideally aims to complete deliver the aircraft back to customer roughly 30 days after input.
A PMI, by contrast, involves extensive maintenance, and is comparable to a “D check” in terms of time taken and scope of work. The aircraft is stripped down for a comprehensive inspection, followed by repairs, repainting and testing. From start to finish, the process tends to take several months.
| MDI (minor depot inspection) | PMI (planned maintenance interval) |
|---|---|
| Every 540 days (bigger check every 1080 days) | Every 6 years (depends on hours flown) |
| Closest to a “B check” | Closest to a “D check” |
| Light checks and engine work | Heavy structural inspection and repairs |
| Short duration (target 30 days) | Lengthy process (several months) |
| No paint strip/repaint | Full paint strip and repaint |
| No components or flight controls removed | Major components and flight controls removed |
| No flight test/short flight test | Engine ground runs and ~4 hour flight test |
In the video, we show aircraft undergoing both MDIs and PMIs at Marshall, though the focus of Chris’ explanation is primarily on the latter, due to the range of tasks carried out.
The key stages of C-130 maintenance
A summary of some of the key maintenance stages outlined by Chris can be found below.
Paint strip
MDI ❌ PMI ✅
Within the first 10 days of an aircraft arriving for a PMI, it is chemically treated to remove all paint and primer until bare metal is exposed throughout the structure. It is then brought into the hangar.
According to Chris, stripping the paintwork will allow the team to conduct a thorough evaluation, “giving them a close look at the detail” and revealing small but critical defects that might otherwise be hard to spot.
Controls and component removal
MDI ❌ PMI ✅
The next stage of a PMI is the removal of flying controls (elevators, rudder, ailerons and flaps) and major external components (including fuel tanks, in-flight refuelling pods, nose cone, landing gear assemblies, and cargo ramp).
Occasionally the team may also need to detach the vertical stabiliser (“tail fin”) or, in even rarer cases, the outer wings. Chris notes that, while this is unlikely, “it’s all possible on a PMI.”
With these controls and components fully removed and stored, the aircraft is prepared for inspection.
Inspection
MDI ✅ PMI ✅
During a PMI, the inspection stage takes weeks or even months. The team thoroughly checks practically every inch of the aircraft, from sheet metal to wiring harnesses, for minor flaws, defects and signs of corrosion using a range of manual inspection methods and non-destructive testing (NDT) techniques.
Throughout this stage, the aircraft will remain on jacks and supports, keeping it in a secure position and allowing for easy access to parts of the undercarriage, including the main landing gear and nose landing gear.
For an MDI, inspections primarily focus on engines. The remaining survey is a straightforward process that (literally) doesn’t extend beneath the surface as the aircraft is still painted.
Parts and repairs
MDI ❌ PMI ✅
Throughout the inspection stage of a PMI, the team records any issues they encounter. This normally results in a detailed list of necessary rectification work, including parts that may need to be repaired, purchased, or fabricated by Marshall on behalf of Lockheed Martin.
Turning this lengthy list into a single, efficient action plan for the aircraft is far from easy: for example, while some actions can happen simultaneously, others need to be completed in sequence.
“It’s a very complex operation,” Chris explains. “If we don’t get the sequencing correct, you could delay the aircraft.”
The puzzle is collectively solved with input from across Marshall’s integrated project team (IPT), which extends beyond the hangars to include engineering, supply chain and in-house manufacturing.
Once the sequence has been determined, the team can provide the customer with reasonably accurate estimate of repaint and delivery dates.
Rebuild
MDI ❌ PMI ✅
Since the bulk of the PMI inspection and repair work is now complete (sometimes several months following input), the team’s focus shifts to returning the aircraft to airworthy state.
The first step is reinstalling and reintegrating large structural components such as flaps or fuel pods that were removed from the aircraft at the start of the process.
Some of these components will already have been painted separately, in which case they are covered in masking material and lined up as neatly as possible to match the anticipated paint scheme on the aircraft body.
Repaint
MDI ❌ PMI ✅
After rebuild, the PMI aircraft is brought into Marshall’s on-site paint barn, which is large enough to house aircraft ranging up to a Boeing 747 or an Airbus 380.
The facility is fully equipped to complete a wide variety of paint schemes and finishes, from simple block colours to high-gloss camouflage—and even complex, showy liveries such as the one Marshall completed for “Fat Albert,” the transport aircraft used by the Blue Angels aerial display team.
The aircraft is repainted, wraps removed and stickers applied before being returned to the maintenance facility for the final stages of the process.
Power, checks and weighing
MDI ✅ PMI ✅
The end of the MDI or PMI is now in site, and the team’s focus is on restoring power to the aircraft.
The team then conducts operational checks, including full and free movement checks to ensure that the flight controls have been rigged correctly, and that there are no obstructions or sources of friction that could potentially affect performance.
The aircraft is also jacked once again to confirm that the main landing gear and nose landing gear retract properly.
On a PMI (but not an MDI), the team also weighs and recalibrates the aircraft, as its centre of gravity may have changed during several of the more invasive stages of the PMI process, including paint strip and repaint.
Engine ground runs and pressurisation runs
MDI ❌ PMI ✅
With flight controls confirmed to be working, the PMI aircraft moves on to ground testing.
Marshall performs engine ground running (EGR) tests in a dedicated enclosure to ensure that the aircraft’s power plants are performing within expected parameters.
This is accompanied by pressurisation checks to ensure that there are no gaps or leaks that could cause a change in pressurisation during flight—particularly important given the number of panels and structures removed during a PMI.
During this process, the aircraft’s computer system will display any fault codes. Once these are rectified, the tests are re-run and the process is repeated until the fault book is clear enough to return the aircraft to customer.
Debrief and functional flight check (FCF)
MDI ✅ PMI ✅
With the MDI or PMI aircraft practically ready to deliver, Marshall contacts the customer, who in turn will prompt their squadrons to dispatch a crew.
Upon arrival of the crew, Marshall provides a maintenance debrief, detailing the work we have carried out.
The crew then has the option of conducting further ground running tests (particularly for a PMI) before proceeding to flight testing.
Flight testing usually takes place a day or two before a customer’s expected departure from Cambridge, and is the customer’s chance to ensure that they are fully happy with the operation of the aircraft before returning it to service. The test itself generally takes roughly four hours following a PMI, and may not be required after an MDI unless flight controls have been disturbed.
When the customer has agreed that the aircraft is fully mission capable (FMC), they formally take delivery, completing the MDI or PMI process.
While the descriptions on this page and in Chris’ video focus primarily on Marshall’s work for the United States Marine Corps, our experience supporting the C-130 platform dates back to 1966.
You can learn more about our C-130 MRO capabilities on our dedicated page, linked below.
Maintenance, Repair and Overhaul
To find out more about the support we provide for other C-130 operators around the world, visit our LinkedIn page.