Manufacturing

Concession

Q: What is the difference between a concession and a deviation?

Timing is the defining distinction. A deviation (also called a deviation permit) is authorized before manufacture begins and grants permission to depart from the drawing for a stated quantity or period. A concession is authorized after the part already exists, dispositioning hardware that was found nonconforming once it had been produced. Both are temporary and bounded: a deviation never alters the master drawing, and a concession applies only to the specific serial numbers or lot listed on it. If the change should become permanent, it must instead go through formal engineering change control to revise the released drawing. In ISO 9001 and AS9100 terms, a deviation is a pre-production permit while a concession is a post-production acceptance of nonconforming output.

Q: Who has the authority to grant a concession on a flight or defense RF component?

For most production nonconformances the material review board (MRB) holds disposition authority, typically a quorum of quality, design engineering, and manufacturing representatives. On defense and aerospace programs the situation is more constrained: when the nonconforming characteristic is a customer-controlled requirement, a major nonconformance, or affects a critical or key characteristic, the contractor's MRB cannot grant a use-as-is concession alone. It must be escalated to the customer or government delegated authority (for example a DCMA or DCAS representative under the contract) for approval before the part can be shipped. Minor nonconformances that do not touch customer requirements can usually be conceded internally, provided the rationale and any limiting conditions are recorded.

Q: Does accepting a concession affect a waveguide component's traceability and warranty?

Yes. A concession does not erase the nonconformance; it documents an informed acceptance of it. The concession number, the nonconforming characteristic and its measured value, the disposition rationale, and any usage limitations become part of the device history record and travel with the serial number. For a precision waveguide flange, that might mean a recorded flatness of 0.004 mm against a 0.003 mm drawing limit, accepted because the gasketed interface tolerates it. Downstream, the conceded condition can restrict warranty coverage of the affected feature, constrain the operating envelope (for example a derated power or a narrower temperature range), and must be disclosed if the customer's contract requires notification of all accepted nonconformances.

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Within a quality-management system, a documented authorization granted after a part is manufactured to use or release it even though it departs from its specified drawing. In RF and microwave production a concession is the "use-as-is" disposition that a material review board applies to a confirmed nonconformance, such as a waveguide flange whose measured flatness exceeds the print limit, when the impact on form, fit, and function is judged acceptable. Unlike a deviation, which is approved before production starts, a concession addresses hardware that already exists, and it never alters the master drawing; it applies only to the named serial numbers and is recorded with the nonconforming value, the rationale, and any usage limits.

Category: Manufacturing

Timing: Post-production

Authority: MRB / customer

The Concession as a Nonconformance Disposition

When an inspector finds that a manufactured item does not meet its drawing, the part is segregated and a nonconformance report is opened. The board reviewing that report has a fixed set of dispositions: rework to bring the part back into specification, repair to a defined acceptable condition, scrap, return to supplier, or accept the part in its existing state. A concession is that last disposition formalized. It is a deliberate decision that the departure, while real, is small enough that the delivered hardware will still perform its intended function, so the cost and schedule of rework or scrap are not warranted. The concession exists so that an engineering judgment of acceptability is captured in writing rather than handled informally on the shop floor.

The economic driver is significant in millimeter-wave manufacturing, where a single precision part can carry dozens of hours of CNC machining, gold or silver plating, and final assembly. A waveguide block at WR-15 (50 to 75 GHz) holds aperture and flange tolerances in the few-micron range, and scrapping a near-complete assembly over a non-critical surface finish or cosmetic plating blemish is expensive. A concession lets quality and engineering release that hardware against documented evidence that the affected characteristic does not control insertion loss, return loss, or mechanical mating, while preserving full traceability of what was accepted and why.

Discipline matters because concessions are bounded by design. Each one applies to a specific quantity or list of serial numbers and expires when those parts ship. A recurring nonconformance that keeps generating concessions is a signal that either the process is incapable or the tolerance is unrealistically tight, and the correct response is a corrective action or a formal engineering change to the drawing, not an endless stream of repeat concessions. Programs track concession rate as a quality metric precisely to surface that pattern.

Concession Versus Deviation Versus Waiver

The three permits are often confused because they all authorize a departure from requirements, but they differ in timing and scope. A deviation is a pre-production permit issued before any affected parts are made. A concession is a post-production acceptance of parts that already exist and were found nonconforming. The word waiver is used in some standards as a synonym for concession (the ISO 9000 family retired the term in favor of concession), and in U.S. defense practice a waiver historically covered nonconformances on items already produced as well. None of the three changes the baseline drawing; a permanent relaxation requires engineering change control.

Acceptance and Quality-Cost Modeling

Whether a nonconformance is worth conceding can be framed quantitatively. The decision weighs the disposition cost against the residual risk, and over a production run the recurring concession rate feeds directly into rolled-throughput yield and the cost of quality.

Concede vs. scrap decision (accept if true):
C_scrap > C_concede + (P_fail × C_field)

First-pass vs. effective yield:
Y_eff = Y_FPY + R_conc (R_conc = conceded fraction)

Functional margin of the conceded feature:
M_func = FL − x̄ (accept only if M_func > 0, even though x̄ > USL)

Where C_scrap = sunk cost of scrapping, C_concede = administrative + risk cost of the concession, P_fail = probability the conceded part fails in service, C_field = field-return cost, USL = upper drawing-spec limit, FL = functional limit beyond which performance degrades, x̄ = measured value of the conceded feature. The point of a concession is that x̄ exceeds USL (the spec margin is negative) yet stays inside FL, so functional margin M_func remains positive. Example: a WR-15 flange flatness of 0.004 mm exceeds the 0.003 mm drawing limit (spec margin −0.001 mm) but stays well inside the ≈0.010 mm flatness at which the gasketed joint begins to leak, leaving M_func ≈ 0.006 mm of headroom, the rationale for the use-as-is acceptance.

Disposition Comparison

Disposition	Timing	Approval Authority	Alters Drawing?	Typical Use in RF Production
Concession (use-as-is)	After manufacture	MRB; customer if critical	No	Non-critical flatness, finish, or cosmetic plating departure
Deviation	Before manufacture	Design + customer	No	Temporary alternate material or tolerance for a known lot
Rework	After manufacture	Quality / MRB	No	Re-machine or re-plate back into specification
Repair	After manufacture	MRB; engineering	No	Bring to a defined acceptable, non-conforming state
Engineering change	Any time	Configuration control board	Yes (permanent)	Relax tolerance permanently when process proves incapable

Common Questions

Frequently Asked Questions

What is the difference between a concession and a deviation?

Timing is the dividing line. A deviation is authorized before manufacture and permits a departure for a stated quantity or period; a concession is authorized after the nonconforming part already exists. Both are temporary, both apply only to a named lot or serial list, and neither alters the master drawing. A permanent relaxation requires formal engineering change control instead.

Who has the authority to grant a concession on a flight or defense RF component?

The material review board usually disposes routine nonconformances. But when the affected feature is a customer-controlled requirement, a major nonconformance, or a critical or key characteristic, the contractor's MRB cannot grant use-as-is alone; it must escalate to the customer or the government delegated authority (for example a DCMA representative) for approval before shipment. Minor, customer-neutral nonconformances can be conceded internally with documented rationale.

Does accepting a concession affect a waveguide component's traceability and warranty?

Yes. The concession number, the measured nonconforming value, the rationale, and any usage limits become part of the device history record and follow the serial number. A conceded WR-15 flange with 0.004 mm flatness against a 0.003 mm limit, for instance, carries that record forward. The accepted condition can limit warranty on the affected feature, derate the operating envelope, and must be disclosed where the contract requires notification of accepted nonconformances.

Related Terms

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