(CNN) -- A pair of commercial jetliners got closer than regulations allow in the skies near George Bush Intercontinental Airport in Houston, the Federal Aviation Administration said Saturday.
The FAA said in a statement that it was investigating Thursday night's "loss of required separation" between planes in airspace controlled by Houston Terminal Radar Approach Control.
At 6:51 p.m., the pilot of Singapore Airlines Flight 61 took off and did not level off at an altitude of 4,000 feet as required, the FAA said.
At the same time, Delta Air Lines Flight 2443 was inbound to the airport at an altitude of 6,000 feet.
"An air traffic controller noticed the deviation and issued traffic alerts and instructions to the pilots of both aircraft," the statement said.
The statement added, "As a result of a preliminary analysis of the event, the FAA has taken steps to ensure that all flight crews are aware of the top altitudes for standard departure routes."