GeoLink: End-of-Life Radio and a Frozen Baseline
GeoLink is a fielded environmental monitoring network with 2,400 deployed sensor nodes and a 12-year support obligation, of which 8 years remain. The node's radio module has received an end-of-life notice; the last-time buy is in 14 months. The module costs $85. An alternative module requires a board respin, new FCC certification, firmware changes, an estimated $620k non-recurring cost plus $110 per unit, and 11 months to first article. The current module's field failure rate is 1.8% per year, and the spares stock is 180 units. The program has no funded obsolescence line. The configuration baseline is frozen under a customer-approved change board that meets quarterly; the next board is in 5 weeks. A last-time buy of 600 units would cost $51k and requires 3 square meters of climate-controlled storage that is not currently allocated.
1. Quantify the spares demand and recommend between last-time buy and redesign, showing your reasoning.
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Annual spares demand is 2,400 x 1.8% = 43.2 units per year. Over the remaining 8 years that is about 346 units, before accounting for attrition, handling damage, and any rise in failure rate as units age. The 180 units on hand cover roughly 4 years at the current rate, so they are insufficient.
A last-time buy of 600 units costs 600 x $85 = $51k and covers about 13.9 years at 43.2 units per year, comfortably beyond the 8-year obligation. Redesign costs $620k non-recurring plus $110 per unit, with 11 months to first article and new FCC certification risk. The unit price difference is irrelevant for existing nodes because no new production is planned at scale; the $620k dominates. Even a modest redesign overrun exceeds the entire last-time-buy cost by an order of magnitude.
Recommend the 600-unit last-time buy as the support bridge, with two conditions: secure the climate-controlled storage, and fund a planned redesign or technology refresh for the next product generation rather than treating the buy as a permanent solution. Also verify the failure-rate assumption; if field returns are trending upward, increase the quantity. The buy is cheap enough that a modest overbuy is better than a shortage that forces an emergency redesign.
2. Describe the change control and configuration management steps required, given the frozen baseline and quarterly board.
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The last-time buy changes the approved spares and support configuration, so it must go through the change board even though the deployed node design is unchanged. Raise an engineering change request with an impact analysis covering cost, schedule, storage, support life, and risk. Include the quantity rationale, the failure-rate and demand calculation, the storage plan, and the exit strategy if the redesign proceeds. The next board is in 5 weeks and the last-time-buy window is 14 months, so the normal quarterly cycle has enough time, but the request should include a trigger for an emergency board if the supplier shortens the window.
On approval, update the configuration baseline: spares quantity, procurement records, storage location and environmental controls, and the supportability plan. Record the module's lot and date codes and require purchases through an authorized distributor to reduce counterfeit risk. Add the obsolescence item to the risk register with an owner and a review date. If the redesign is also approved, create a separate change request for the board respin, firmware, and certification, and keep the two changes distinct so the bridge buy is not delayed by redesign decisions.
3. Identify the risks created by the last-time buy and the mitigation for each.
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First, storage degradation: modules sitting for years can suffer moisture absorption, solderability loss, and corrosion. Mitigate with climate-controlled, ESD-protected storage, sealed packaging with desiccant, humidity monitoring, and a first-in-first-out policy that rotates stock into field replacements.
Second, counterfeit and quality risk: a single large lot from an unauthorized source can be worthless or unsafe. Buy only through the authorized distributor or the original manufacturer, retain lot traceability, and sample-test incoming units. Third, technology lock-in: the buy keeps a dying module in the support chain for up to a decade and may become unrepairable if the firmware toolchain or test fixtures disappear. Mitigate by archiving firmware, tools, and test procedures with the spares, and by funding a technology refresh plan.
Fourth, demand uncertainty: the 1.8% failure rate may rise as units age, making 600 units insufficient. Set a review trigger, for example if annual returns exceed 60 units, and consider a larger buy. Fifth, the unfunded storage and procurement cost: obtain a funding line before committing. Document all of these in the risk register with owners and dates.