The Static-Port Repair: An RVSM Decision That Costs an Aircraft
An RVSM static port repair is where the whole framework is tested, because it is the one place where a technically excellent piece of work can quietly destroy an approval. What follows is an illustrative scenario — the aircraft, the damage and the dimensions are invented to make the decision chain visible — but the chain itself is real, and so is the way it breaks.
The scenario
A regional jet arrives on a night shift with corrosion damage to the fuselage skin. For the purposes of illustration, say the damage sits roughly 15 centimetres from the left static port; the actual boundary that matters is whatever the aircraft’s instructions for continued airworthiness define, and it is not a number you may generalise between types. The aircraft is required on an RVSM route the following morning.
A licensed technician carries out a blend-out to the general section of the Structural Repair Manual. The repair is sound. It is inspected, certified and recorded correctly. The aircraft returns to service and flies its route.
Some weeks later the operator is notified of an altimetry system error beyond the SPA.RVSM.115 threshold on that airframe. It has 72 hours to report to the competent authority with an initial analysis of causal factors and the measures taken to prevent repeat occurrences, and the aircraft comes out of RVSM service while the position is regularised.
Nobody was negligent. The repair was good. The decision around the repair was never made.
What the framework actually required
Two provisions sit directly on this scenario, and neither is about repair quality.
AMC1 ACNS.A.GEN.010(b)(2) provides that any repairs, not covered by approved maintenance documents, that may affect the integrity and accuracy of the altimeter system — for example those affecting the alignment of pitot/static probes, repairs to dents or deformation around static plates — should be subject to a design review which is acceptable to the competent authority. AMC1 ACNS.A.GEN.010(b)(3) provides that airframe geometry or skin waviness checks should be performed following repairs or alterations which have an effect on airframe surface and airflow.
The corresponding operator-facing text in Part-SPA of Regulation (EU) No 965/2012 is AMC3 SPA.RVSM.105(b), which requires continuing airworthiness procedures establishing a process to assess any modification or design change which in any way affects the RVSM approval; to evaluate any repairs that may affect the integrity of the continuing RVSM approval, for example those affecting the alignment of pitot/static probes, repairs to dents, or deformation around static plates; and to ensure the proper maintenance of airframe geometry for proper surface contours and the mitigation of altimetry system error, surface measurements or skin waviness as specified in the instructions for continued airworthiness, to ensure adherence to RVSM tolerances.
Two things follow. First, the general SRM section the technician used was approved data — for structure. It said nothing about the altimetry consequences of working next to a static plate, because that is not what it is for. Second, and this is the framing correction that matters: none of the text above is addressed to the CAMO or to the Part-145 organisation. It is addressed to the operator, who holds the RVSM approval. Yet the operator cannot possibly discharge it. The assessment, the routing to a design organisation, the contour measurement and the withholding of the aircraft from RVSM service are all continuing airworthiness and maintenance activities. The operator’s approval is only as good as the process the CAMO wrote for it — which is precisely why AMC1 SPA.RVSM.105 requires the application to include the aircraft maintenance programme and continuing airworthiness procedures in support of the RVSM operations.
The decision chain, and where it breaks
| Step | Question | Failure mode on the night shift |
|---|---|---|
| Technician, before starting | Does this damage sit in an area the ICA treat as RVSM-significant? | Nobody has been told where that area is; the SRM does not flag it |
| Technician | Is the intended repair covered by approved maintenance documents for this location and this effect? | A general structural section is treated as covering a location-specific altimetry question |
| CAMO | Does this repair require a design review acceptable to the competent authority? | The repair is never routed to the CAMO at all |
| CAMO | Does the ICA require an airframe geometry or skin waviness check afterwards? | No task exists in the programme, so nothing is raised |
| CAMO | Is the aircraft withheld from RVSM operations until the checks pass? | No RVSM serviceability status is tracked separately from the CRS |
| Operator | Is a reportable height-keeping error being managed within 72 hours? | Handled correctly — weeks too late to matter |
Look at the failure column. Not one entry is a competence failure or a workmanship failure. Every one is a documentation and process failure — a missing task, a missing routing rule, a missing status field. That is why we treat RVSM as a maintenance-programme subject first, as set out in what the CAMO must build into the RVSM maintenance programme, and why the ownership question in why RVSM is a maintenance problem, not just an operations one is not academic.
Why the geometry matters at all
Because the corrections are built around the shape. AMC1 ACNS.E.RVSM.030 provides that if the design and characteristics of the aircraft and its altimetry system are such that the performance requirements are not satisfied by the location and geometry of the static sources alone, then suitable Static Source Error Corrections should be applied automatically within the altimetry system. The performance the installation has to hold is exacting — CS ACNS.E.RVSM.030 requires the automatic altitude control system to control the altitude within ±20 m (65 ft) about the selected altitude in straight and level flight under non-turbulent, non-gust conditions. A doubler sitting slightly proud is not a trivial cosmetic matter against that background. The mechanism is set out in more detail in skin waviness, static ports and the hidden geometry of RVSM.
One number to stop misquoting
In scenarios like this, engineers reach for ±75 m (±245 ft) and call it the certification limit. It is not. SPA.RVSM.115(a)(2) sets it as an operational reporting trigger for an individual aircraft. The certification criteria are separate and are in CS ACNS.E.RVSM.035: for group aircraft, throughout the full envelope, ASEmean shall not exceed 25 m (80 ft) and ASEmean plus three standard deviations shall not exceed 60 m (200 ft); for non-group aircraft, 50 m (160 ft) in the basic envelope and 60 m (200 ft) in the full envelope. No 75 m figure appears in CS ACNS.E.RVSM.035. The consequence for our scenario is uncomfortable: an aircraft can be performing well outside what its type was certified to deliver and still not have crossed the reporting trigger. See RVSM height monitoring and error reporting for the full comparison.
The position if the chain has already been broken
If a repair that may affect the integrity and accuracy of the altimeter system has been embodied without a design review acceptable to the competent authority, and no airframe geometry check was performed, then in our view the honest engineering position is that continued compliance with the RVSM tolerances is not demonstrated. It is not that the aircraft is proven non-compliant; it is that nobody can show it is compliant, and RVSM is an approval built entirely on demonstrable evidence. We would expect a competent CAMO to withhold the aircraft from RVSM operations, obtain an accepted repair scheme, perform the geometry and static system checks, and record the whole sequence — rather than wait to be told by a monitoring result.
Where that discipline lives, in document terms, is the exposition. Our guidance on how to write a CAME and on building a CAMO management system covers where a repair and modification RVSM assessment route belongs, and the consolidated rule text is in the EASA Easy Access Rules. If you would rather have your engineers make this decision correctly the first time, that is what our RVSM maintenance training for CAMO and Part-145 personnel course is built to do. The cost of skipping the review is an aircraft out of service and a report to the authority. The cost of doing it properly is one phone call and a contour check.
Frequently asked questions
Does every repair near a static port need a design review?
AMC1 ACNS.A.GEN.010(b)(2) applies to repairs not covered by approved maintenance documents that may affect the integrity and accuracy of the altimeter system, giving as examples those affecting the alignment of pitot or static probes and repairs to dents or deformation around static plates. Where approved data covers the repair, that design review route is not triggered by this provision; where it does not, it is.
What must the continuing airworthiness procedures cover for RVSM repairs?
AMC3 SPA.RVSM.105(b) requires a process to assess any modification or design change which in any way affects the RVSM approval, to evaluate any repairs that may affect the integrity of the continuing RVSM approval, and to ensure the proper maintenance of airframe geometry for proper surface contours and the mitigation of altimetry system error, surface measurements or skin waviness as specified in the instructions for continued airworthiness.
Who reports the resulting height-keeping error?
The operator. SPA.RVSM.115 places the duty on the operator, within 72 hours, with an initial analysis of causal factors and measures taken to prevent repeat occurrences. In practice the causal analysis is a maintenance investigation carried out by continuing airworthiness and maintenance staff.
Is 245 ft of altimetry system error a certification limit?
No. It is the individual-aircraft reporting trigger in SPA.RVSM.115(a)(2). CS ACNS.E.RVSM.035 sets the certification criteria at 25 m (80 ft) for ASEmean and 60 m (200 ft) for ASEmean plus three standard deviations for group aircraft throughout the full envelope, and 50 m (160 ft) basic envelope and 60 m (200 ft) full envelope for non-group aircraft. No 75 m figure appears in CS ACNS.E.RVSM.035.
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