July 16 (Reuters) - Spirit Airlines on Tuesday cut its revenue outlook for the second quarter, citing lower-than-expected non-ticket revenue, sending its shares down more than 6% in extended trading.

The company now projects quarterly revenue to be $1.28 billion, compared with its earlier estimate of between $1.32 billion and $1.34 billion, the ultra-low-cost carrier said in a regulatory filing.

Spirit said lower non-ticket revenue from ancillary services was a result of competitive pressures in the market.

The non-ticket revenue per passenger segment is estimated to be $64, "several dollars" below its initial expectations.

Additionally, Spirit estimates $37 million in AOG (aircraft on ground) credit from Pratt & Whitney. The airline gets a monthly

credit

as compensation for Spirit being unable to use aircraft with engine issues. (Reporting by Pratyush Thakur in Bengaluru; Editing by Maju Samuel)