A Frontier Airlines crew fell ill mid-flight on Thursday, prompting the pilots of Flight 1046 to declare a medical emergency shortly before landing in Florida.

Four flight attendants on the service from Cleveland to Fort Lauderdale-Hollywood International Airport developed headaches and nausea as the aircraft neared its destination. The pilots asked air traffic controllers to arrange for emergency medical personnel to meet the Airbus A321 at the gate, according to air traffic control communications reported by PYOK. Having responders meet an arriving aircraft at the gate is a standard safeguard when crews report in-flight illness, allowing medical care to begin as soon as the plane parks. Frontier, a Denver-based ultra-low-cost carrier, operates an all-Airbus fleet of A320-family jets.

The plane touched down at Fort Lauderdale-Hollywood International Airport without incident, and emergency responders were waiting when it arrived, the outlet reported.

As the aircraft approached South Florida, one of the pilots alerted controllers to a "developing medical" situation on board.

"If you could call the tower and have them meet at our gate for a developing medical," the pilot said in the radio call.

Pressed on the nature of the emergency, the pilot said multiple flight attendants were experiencing symptoms.

"All my flight attendants have headaches, and now three, now four, are nauseous," the pilot said.

The 10-year-old Airbus A321 departed Cleveland shortly before 8 a.m. on Thursday. It had been scheduled to fly back to Cleveland at 11:30 a.m., but the return flight was canceled, according to PYOK. No reason for the cancellation was given in the report.

The cause of the illnesses was not immediately known, and the flight attendants' conditions after landing were unclear. When several crew members report similar symptoms at once, airlines and regulators in past cases elsewhere in the industry have examined the cabin air supply, which on A320-family aircraft combines engine bleed air with recirculated air passed through high-efficiency particulate air filters. Flight attendant unions, including the Association of Flight Attendants, have for years pressed for stronger monitoring and reporting of such in-flight illness episodes. No suspected cause has been indicated in this case.

The airline's response, the crew's conditions, and the reason the return leg was canceled remain open questions. FOX Business has reached out to Frontier Airlines for comment.