Earlier this year, air traffic controllers working a graveyard shift for Newark Liberty International Airport noticed a strange phenomenon. Phantom aircraft were populating one of their radar screens.

“False targets” kept showing up in one airspace map “throughout the night,” one employee recounted in an incident report.

Controllers for Newark have also experienced a spate of unnerving equipment outages this year. In one instance, the radio feed connecting pilots with the controllers was marred with static. When controllers tried to use a backup line, they found that it wasn’t working at all.

On another occasion, automatic alerts attached to a weather-detection system that flagged gusty and sometimes dangerous conditions known as “wind shear” were not working.

These incidents, which have not been previously reported and were discovered in a review of government documents by The New York Times, occurred over the months before and weeks after a massive outage took down both radar scopes and radio contact with pilots simultaneously on April 28 — scaring controllers, causing delays, canceling flights and frustrating the flying public.

The records reviewed by The Times reveal previously unknown glitches this year that point to a more profound problem with air-traffic control technology in the Philadelphia tower that handles much of the traffic for Newark than even the outage in April and others in May have suggested.