The previous day saw more than 11,300 services delayed or cancelled, in the first national grounding of air traffic in two decades.
A computer failure at the Federal Aviation Administration prevented airports from filing required safety notices, bringing flights to a halt.
That spelled chaos for passengers across the country:
"Maybe they need to just reset the FAA button, or unplug and re-plug."
FAA officials say a preliminary review traced the problem to a damaged database file.
They said there was no sign of a cyberattack.
Reuters sources say the same file corrupted both the main system and its backup.
A probe into the events is now ongoing.
Major carriers such as Delta, United and Southwest all said they expected normal operations on Thursday.
Now the Senate Commerce Committee has promised to investigate the incident.
Republican lawmaker Ted Cruz called it "completely unacceptable".
Some experts also expressed concern over the health of the FAA, which faces a leadership vacuum.
It's been without a permanent administrator since March.
The Senate has not held a hearing on President Joe Biden's pick to head the agency.
