One Manhattan power room took down FAA air traffic control in 1991

On September 17, 1991, a -48 V DC power plant on the 20th floor of 33 Thomas Street, an AT&T switching hub, lost its AC-to-DC rectifiers during a 10:10 a.m. transfer from Con Edison to diesel generators after a voltage spike tripped an overload relay that had been misadjusted during modernization. The rectifiers opened and the lead‑acid KS‑20472 battery strings on the AT&T Lineage 2000 bus picked up the full load for the building’s high‑capacity DS3 transmission bays, holding voltage on a flat battery plateau for over six hours. Because every primary and backup FAA landline serving New York TRACON and the Kennedy, LaGuardia, and Newark towers ran through those bays, the batteries’ sudden collapse at 4:40 p.m. wiped out radar feeds, primary radios, and automated flight‑handoff links, forcing controllers onto short‑range backups and resulting in 1,174 delayed or canceled flights and a multi‑hour recovery.

The outage stemmed not from a single hardware fault but from four linked operational failures: a burned‑out indicator lamp, a missing 25‑inch jumper strap in the 14th‑floor alarm base, an alarm bell mechanically muffled, and an unexecuted watch handoff while DC staff attended off‑site training and no remote telemetry existed. A late attempt to cut rectifiers back failed because the deeply discharged battery bank would not accept recharge under full load and the plant lacked automatic restart capability. The incident demonstrates how misadjusted protection, degraded alarms, muted audible warnings, absent monitoring, and deficient restart procedures combined to turn a routine generator transfer into a regional aviation crisis.