The Spirit Airlines website has crashed, leaving customers unable to book flights online.

The discount airline calls the problem “intermittent.”

Spirit gave no indication online Wednesday when the problem will be fixed or what caused it. A company spokesman said a partial outage was quickly fixed but another started 40 minutes later. He said flights were not affected.

Computer outages are not unusual at airlines. Most carriers operate IT systems that are a mix of old and new applications, making them more vulnerable to problems.

Spirit is based in Miramar, Florida. It is a low-fare carrier that relies heavily on extra fees for revenue and primarily serves leisure travelers.

(AP)