Airlines will be in focus on Friday as we find out if US consumers can complain about prices and book flights. Airline stocks have been surprisingly strong preformers this year despite a heavy headwind from rising fuel costs and interest rates.The question heading into Delta’s third-quarter earnings report on Friday, October 9, before the opening bell is whether the consumer continuse to remain strong. The conference call comes at 10 am ET, and that’s where I’ll be listening for clues about how much more consumers are willing to pay.Summer travel is behind us but Boomers are increasingly traveling in the shoulder seasons and corporate demand is reportedly strong. What matters now is whether demand holds through the holidays and whether airlines can keep passing along higher fuel costs without emptying seats.Management set a strong revenue bar in July, forecasting mid-teens year-over-year growth on modest capacity growth, with revenue per available seat mile improving sequentially. Delta also guided to adjusted earnings of $2.00–$2.50 per share and an operating margin of 11–13%. At the time, management said booking trends offered a constructive setup for strength to continue into the December quarter.That last point is the one I want tested tomorrow.For context, Refinitiv estimates cited this week put adjusted earnings at $1.75 per share, below management’s original range. That suggests investors are already braced for some pressure on profitability. A backward-looking earnings miss would therefore need to be weighed against what Delta says about the next three months. Some numbers to watch:Q3 adjusted EPS:$1.75, versus $1.71 a year ago and management guidance of $2.00–$2.50.Q3 revenue:$17.671 billion, up 16.3% year over year, versus guidance of $17.325–$17.629 billion.Q3 EBITDA:$2.381 billion, versus $2.309 billion a year ago.Q3 EBIT:$1.700 billion, versus guidance of $1.906–$2.292 billion.Q4 consensus: EPS of $1.32 on revenue of $17.326 billion.Full-year consensus EPS:$5.33, well below management’s $6.50–$7.50 guidance.Fuel is the obvious complication. Delta’s July outlook assumed an all-in September-quarter fuel price of approximately $3.15 per gallon, based on the forward curve on July 2 and including a small refinery benefit. That makes the updated December-quarter assumption particularly important.I’ll be looking for how much of the fuel increase Delta expects to recover through fares, how quickly that recovery happens and whether its margin guidance requires energy prices to ease. Also note that CEO Ed Bastian spoke in an interview on October 6 and said “there’s no slowdown in sight" on the booking curve, highlighting that 95% of its revenues came from households earning at least about $100,000 per year.On demand, I want detail beyond a reassuring headline about bookings. Are Thanksgiving and Christmas filling at higher fares? The travelers at those times of year are likely to be the less affluent. Are customers booking later, trading down or becoming more responsive to discounts? Is strength broad across domestic leisure, international travel and corporate accounts?Delta’s premium business also deserves attention. Premium revenue rose 17% in the June quarter, but tomorrow’s read-through will be stronger if ordinary main-cabin customers are holding up alongside those buying more expensive seats.For markets, resilient bookings and credible fuel recovery would support the case that household spending still has momentum. Softer demand alongside stubborn fuel costs would be a much less comfortable combination.As for the share price, Delta has been surprisingly strong this year, rising 20% YTD versus -3.5% for United and -18% for American. We will see how markets react. This article was written by Adam Button at investinglive.com.