Welcome to Waypoint A.2. We are discussing Electrostatic Discharge Sensitive (ESDS) devices. In the world of modern avionics, invisible static electricity is a silent killer of components. As defined in the AMC 20-22 syllabus, we need to understand the sources of ESD, the types of failures, and the procedures to prevent them.

First, let’s identify the sources of electrostatic discharge. It’s not just lightning or major electrical faults. It’s you. Walking across a carpeted flight deck can generate 12,000 volts. Sliding off a fabric aircraft seat can generate 6,000 volts. Yet, it only takes 10 to 30 volts to damage a sensitive microchip. You cannot feel, hear, or see a discharge less than 3,000 volts. This means you can destroy an LRU without ever knowing you touched it.

We categorize ESD damage into two types: Soft Failures and Hard Failures. A Hard Failure is immediate—the component stops working right there on the bench or the aircraft. Ironically, this is the “good” type of failure because we know it’s broken. The dangerous one is the Soft Failure. This is where the component is weakened but still functions. It passes the BITE check. It flies. But it will fail weeks or months later, usually under stress—like during approach in bad weather. This causes intermittent faults (NFF – No Fault Found) that plague our maintenance schedules.

To prevent this, we adhere to strict ESDS safety procedures. In the workshop, this means grounded conductive mats and wrist straps. On the line, specifically for Part-145 engineers, it means you must bond yourself to the airframe before touching the connector pins or the ESDS unit. Never touch the pins of a connector with your fingers. Oils and static are a bad combination.

Finally, let’s talk about handling and packing. ESDS components must always be transported in conductive packaging—those silvery or black bags you see. Pink poly is anti-static (it doesn’t generate charge) but it does not shield against external fields. Only the conductive shielding bags provide full protection. Never transport an LRU or circuit card loose in a tote tray or a pocket. If you remove a unit from the aircraft, the caps go on immediately, and it goes into the ESD bag immediately.

Treat every avionics computer as if it were a fragile egg. Static is the invisible hammer.