A steam cleaner arrives in an aircraft maintenance discussion as a question about cleaning, but the answer turns on the hangar around it. A fuselage is a large, mixed-material surface pierced by probes, vents, seams and drain paths, and it is cleaned between inspections under records rules. Before anyone asks whether steam can be used on an aircraft, the useful question is whether the hangar can run the method repeatably: where the water goes, which parts may not be sprayed, what the wash bay does with the runoff, and how the task is written down so that the next shift does it the same way.
Split the task before choosing the machine
A maintenance wash is not one surface. The exterior skin, the nose and landing gear areas, the wheel wells, the interior panels and the ramp-side tarmac around the aircraft behave differently, and each one has its own limits. Write the task list surface by surface, with the soil you are trying to remove named for each: hydraulic fluid and rubber deposits around gear, dust and film on skin, grease near fairing fasteners, spills in the cabin. Only then does it become clear which part of the job a steam process is being asked to do, and which part stays with the current method. This split is what most proposals skip, and it is the reason so many cleaning trials end with a machine that nobody can describe afterwards.
Keep the wording honest in the list. If a task was previously done by hand wipe, solvent wipe or a pressure wash, write that down as the baseline. Cleaning comparisons only become useful when the existing method is described with the same care as the new one.
Write the no-spray list first and have it signed
Before any lance leaves its holster, the aircraft-side items that must not be sprayed should be listed and signed by the maintenance lead who owns the airframe, not by the cleaning crew. On a light aircraft this normally includes pitot probes and static ports, antenna bases and heated probe covers, avionics and equipment bay openings, vent and drain holes, wheel-well cavities and gear leg seams, windshield and window seals, door and fairing seals, and any area where a repair, patch or re-fastening was done recently. The list is also the place to record which openings are covered, by whom, and how coverage is removed and re-checked at the end.
Ask the supplier what their own documentation says about these exclusions. A machine described as high temperature and high pressure is not thereby suitable for every surface on an airframe, and a supplier who cannot name what they would avoid spraying is a supplier who has not worked around aircraft.
Surface condition decides more than the machine does
Heat and pressure change the result depending on what is underneath. Bare metal, painted skin, clear-coated panels, composite panels with a thin outer layer, anodised fittings and older repairs all react differently to hot wet cleaning, and none of that can be judged from a catalogue. Treat coatings and finishes as the variable, and run a trial on a small, low-consequence area, on a panel that can be left out of service, or on a spare skin section if one exists. Let it dry fully before judging, then look for blistering, colour shift, lifting at edges and residue in lap seams. A judgement made on a wet surface is not a judgement.
Photograph the trial area from a fixed angle before and after, and keep the photographs with the maintenance record rather than in a supplier's sales folder. If the trial fails, that record is worth more than a successful one, because it tells the next buyer what the limits are.
Water is the constraint, not steam
Steam is often proposed because it uses less water than a hose. That matters in a hangar where the floor drains into a separator, or where there is no drain at all in the bay. The practical questions are: where is the nearest tap with the right fitting, how far is the walk from the machine to that tap, how many refills does one aircraft need, and where does the runoff go once it has picked up oil, hydraulic fluid and dust off the airframe and the ramp. Runoff that leaves the building is a drainage question, not a cleaning question, and it should be settled before the trial, with the interceptor or collection point checked so it is not overwhelmed by the wash.
Ask the supplier to describe the method in terms of water per hour at a stated lance distance, number of passes and dwell time. If they will only give a marketing description of cleaning power, the number has to be measured on your own aircraft with your own staff, and that is a cost to plan for rather than an accident.
Where the aircraft sits matters too. Standing water on the floor, on cowlings or in cavities extends the time before the aircraft can be released, and standing water near a wheel well is a slip hazard for everyone walking the inspection. A method that saves water but leaves surfaces wetter for longer has not saved anything.
Utilities belong to the bay, not to the brochure
Fixed equipment needs a power circuit at the position where the work actually happens, a water inlet that matches the machine, and enough floor area around it for the operator to stand, move and hose without crossing a walkway or an aircraft tow path. The PowerDe HW02 steam cleaner product page, for example, lists 220 V working voltage, 6 kW heating power, an 80 L SUS304 tank and a 1/2 inch tap-water inlet with a 4-point internal-tooth joint. Those figures are installation conditions for one fixed machine; they are not a claim that any particular airframe surface can be cleaned by it. Ask, for each machine in the quote, which adapter is supplied with the inlet, whether the tank size means one refill or several per aircraft, and where the cable will run so it never crosses the area the aircraft is moved through.
A mobile unit moves the utility question to the battery and to the walk to the tap. Either way, walk the route before agreeing, and write the distance down. It is usually the walking and the refilling, not the spraying, that decides whether the task fits inside the window the hangar can release.
Fit the task to the hangar window, not the reverse
Aircraft cleaning happens in the gaps: after a check, before a release, during a heavier maintenance visit, or in a seasonal deep clean. Group the work by window rather than by aircraft. A quick ramp-side clean between bookings is a different scope from a full exterior clean during a 100-hour inspection, and both need their own task list, coverage list and drying allowance. Freeze the parameters for each window before the trial: the mode, the nozzle, the distance, the travel speed, the number of passes and the dwell time. If the numbers change between the trial and the routine job, the trial told you nothing.
Compare against your own baseline, not against a supplier's expectation. Time the current method on your dirtiest aircraft with your own people, and record the same measurements for the new method: minutes of lance time, number of refills, walking distance to water, and how long surfaces take to dry before the aircraft is handed back. Those four numbers are what make a decision defensible inside a maintenance organisation.
Records, and who signs what
Cleaning an airframe sits inside a documented process. Whoever signs the release needs to know what was applied, to what, with what coverage in place, and what was inspected afterwards. One line per aircraft is enough: date, aircraft, areas cleaned, mode and nozzle, who sprayed, who checked the coverage removal, and any finding. Where the cleaning is part of an inspection task, agree with the maintenance lead which steps the signatory inspects before the aircraft goes back into service.
Put the machine itself into the maintenance plan as well. Tap water leaves scale in heaters and generators, and scale shifts output over time, so a drift in flow is a maintenance symptom rather than a cleaning failure. Name the person who owns descaling, agree the wear parts with part numbers and lead times, and keep the cleaning parameters and the machine maintenance in one controlled document, so the two cannot drift apart.
Where it does not fit
A steam process is the wrong choice when the no-spray list covers most of the area to be cleaned, when there is no way to collect the runoff, when the window is too short for surfaces to dry, or when the surface condition is unknown and cannot be trialled. It is also the wrong choice if the organisation has no one who will sign a written method; without that, a machine becomes an improvised tool and the trial result cannot be reused.
If the bay does not match a standard configuration, ask about customized steam cleaning equipment as a finding from the site survey rather than as an assumption at the start. The survey output is the request: surface list, signed no-spray list, photographs, the four measured numbers, and the drainage facts for the bay.
A short buying checklist
Send the surface and soil list, the signed no-spray list, the fixed-angle photographs, the measured baseline, and the power, water and drainage facts for the bay; ask for mode and nozzle, expected water per hour at the stated settings, tank capacity, inlet fitting and adapters, required supply, and a wear-parts list with part numbers and lead times. Read the replies for what is answered, leave blanks blank, and do not infer missing values. More on the range of cleaning equipment is listed on the PowerDe cleaning pages, and contacting PowerDe with the survey pack is a faster way to test whether a supplier can work to an aircraft-hangar brief than a catalogue search.
