Steam cleaning is now offered for airframe exteriors, but an aircraft operator assessing it has no product catalogue to argue with - they have a maintenance programme, a hangar window, and a person who signs the release. The useful question is not whether steam "works" on an aircraft, because that sentence proves nothing. The question is what an assessment has to produce before the first nozzle touches an airframe: a written scope, a signed exclusion list, a trial with fixed parameters, and a set of measurements the operator already owns.
Define the task before assessing any equipment
"Exterior clean" covers several different jobs with different effort profiles: a routine film removal on a light airframe, a bug and organic residue removal after seasonal operations, oil and hydraulic-fluid staining around fairings and landing-gear bays, and a cosmetic clean before a lease return or a sale. Each has a different pass criterion, and an assessment that averages them is worthless. An operator scoping aircraft exterior cleaning equipment should expect that surface-group split to appear in the supplier's own site survey before any model number is discussed. Start by writing the task down at the level of surface groups - painted aluminium, bare or anodised metal, composite panels, glazed surfaces, decals and registration markings, lip seals and window surrounds, gear bays and wheel wells, skin joints and lap seams, static ports and probes, antennas and static dischargers - and note which of those groups the current method already handles and which drives the cost.
A supplier cannot respond to a picture of a dirty airframe. They respond to a scope: surface groups, the soil on each group, how long it has been there, what has already been tried, and what the finish is expected to look like afterwards. If that document does not exist, the assessment will be settled by whoever talks loudest, not by evidence.
The exclusion list is a precondition, not a caveat
On an airframe, the constraint is almost never the panel; it is everything built into the panel. Before any trial, list the openings and assemblies where directed water and heat are not acceptable: static ports and pitot assemblies, static wicks and antenna bases, cabin and cockpit windows with their seals, door and baggage-compartment lip seals, skin joints, lap seams and fastener lines with sealant, access-panel edges, landing-gear bays with their wiring runs and connectors, brake and axle areas, cooling and vent openings, and any area with an existing repair, touch-up, or open documentation. That list should be written by - and signed by - the person accountable for the airframe's airworthiness status, not decided at the wand by a cleaning contractor.
Two further conditions belong in the same document. If the coating, finish or repair history of a panel is unknown, treat it as out of scope until someone with coating authority says otherwise; a trial on a test panel that is not representative tells you nothing. And any cleaning that could disturb a repair, a bonded doubler, or a sealing joint needs the same release discipline as any other maintenance task. A cleaning method that cannot be written into that discipline is not assessable - it is simply unavailable to your operation.
Equipment literature can support the safety argument only so far. Published specifications for a fixed machine rated at 220 V working voltage with 6 kW heating power and an 80 L SUS304 tank - the PowerDe HW02 listed at the link below - include protection functions such as leakage, short-circuit, high-temperature, high-voltage and water-shortage protection. Those names describe how the machine behaves when something is wrong; they are not statements about what a spray does to a lap joint, and they do not transfer approval from your organisation to the machine.
Run a trial that can be compared with today's method
Assessment means comparison, and the honest comparator is the method you use now, on the same airframe, in the same window, with your own staff. Fix the parameters before the trial and record them: which mode is used, nozzle type, distance from the surface, travel speed, number of passes, dwell time, whether a detergent is used and at what dilution, and in what order the surface groups are worked. Then measure four things you can obtain without instrumentation - time per surface group, number of stops for refilling or reheating, distance walked to the water and power points, and the interval before the aircraft can be released for the next task.
Define the pass criteria before the trial, not after it. For an airframe these are usually inspection criteria: no residual film on the treated group, no water pooling in a joint, gap or bay, no visible change to a coating or decal after drying, seals and drainage paths confirmed clear, and the exclusion list re-checked item by item. Write them as observations somebody can confirm on a dry airframe, and keep a fixed-angle photograph of each group before and after - not for marketing, but so that the second trial is comparable to the first.
Hangar utilities decide whether the method is usable
Most exterior-cleaning assessments fail on ground support, not on cleaning. A fixed steam cleaning machine such as the PowerDe HW02 is positioned on floor area, needs a protected power outlet on a suitable circuit, and takes tap water through a 1/2 inch four-point internal-tooth inlet - so the run of cable across a wet apron and the distance to a potable water point are part of the labour cost, not an afterthought. A machine that must be moved, or whose hose cannot reach the far side of the airframe without dragging across a walkway, will quietly change the schedule.
Water that leaves the airframe has to go somewhere, and an apron or hangar floor is not a drain. Where runoff is collected, how it is intercepted, who owns the drainage route, and how the floor is dried before movement is resumed all belong in the assessment. So do the freeze or wind limits of the working window, the availability of a covered bay, and whether the same window is needed for inspection, fuel or maintenance tasks. An assessment that reports cleaning quality while ignoring the drain and the bay booking is not an assessment of a method - it is a demonstration.
Documentation and records stay with the operator
Steam on an airframe produces records whether or not anyone plans to keep them: what was treated, what was excluded, what parameters were used, who released the aircraft, and what was found after drying. If your organisation cannot attach those facts to the aircraft's maintenance records in the form your quality system expects, then the method cannot be adopted at fleet scale regardless of how the panel looked. Before assessing equipment, confirm who inside your organisation owns that documentation and what form they require.
A practical sequence works better than a specification debate. First, one airframe with a known soil problem, one surface group, and one written pass criterion. Second, the trial with parameters frozen and the four labour measures recorded. Third, a review against the current method, including what had to be excluded. Only then does the equipment question become answerable, and only then can the specification of a PowerDe HW03 fixed steam cleaning machine be compared with what your bay can actually supply, instead of being read as a promise about your airframe.
What a credible supplier should be able to provide
Ask for the boring things in writing. Which mode the machine offers and what each mode changes about water loading on the surface. Published electrical and water connection details so your facilities team can confirm what the bay can actually supply. The protection functions the machine is specified with, and the maintenance tasks - including scale control and nozzle inspection - that keep those functions meaningful. Spares, consumables and lead times. And a willingness to have the trial witnessed by your own staff on your own airframe. A supplier who answers with a single performance claim, and cannot discuss exclusions, drainage, or the records your organisation must keep, is describing a product; you are trying to assess a process.
If the trial is worth running, send the scope document, the exclusion list, the fixed-angle photographs and the four labour measures, and let the site survey - not the model number - drive the quotation. Use the contact page to start that conversation with the operational facts already in it.
