American Airlines Group Inc. /zigman2/quotes/209207041/composite AAL +3.82% disclosed Wednesday that financial costs related to the groundings of its 737 MAX jets, made by Boeing Co. /zigman2/quotes/208579720/composite BA -1.19% , "cannot be forecasted at this time," as it remains dependent on a number of still-unknown factors. The stock rose 1.5% in premarket trade, as shares of rival United Continental Holdings Inc. /zigman2/quotes/205037281/composite UAL +1.99% rallied 2.9% after the carrier reported late Tuesday fiscal fourth-quarter earnings and revenue that beat expectations. The airline operator said the factors include the period of time the aircraft are unavailable and the circumstances surrounding the reintroduction of the jets once the grounding is lifted. The company announced earlier this week flight cancellations through Aug. 19, assuming its MAX 8 fleet would not be available through then. American said it its fleet currently includes 24 MAX 8 aircraft, with an additional 76 aircraft on order from Boeing. American's stock has edged up 1.3% over the past three months through Tuesday and the NYSE Arca Airline Index /zigman2/quotes/210598447/delayed XX:XAL +2.81% gained 2.1%, while the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.64% hiked up 10.3%.