Over the past few months, the grounding of the Boeing 737 MAX has forced several major U.S. airlines to reduce their domestic capacity. That has paved the way for strong revenue and profit growth at airlines that haven't been affected by the 737 MAX grounding. Delta Air Lines recently reported stellar results for the second quarter, and a couple of other airlines raised their quarterly forecasts last week.

As a result, many investors hoped for guidance increases at JetBlue Airways (NASDAQ:JBLU) and Spirit Airlines (NYSE:SAVE), neither of which operates the 737 MAX. Instead, both carriers reaffirmed their recent forecasts last week. However, JetBlue and Spirit remain on track for strong earnings growth in the second quarter and beyond.

JetBlue finalizes its unit revenue outlook

Back in April, JetBlue projected that revenue per available seat mile (RASM) would increase 1% to 4% year over year in the second quarter, after falling 3.1% in the first quarter. Last month, the carrier boosted the low end of its Q2 guidance range, saying that RASM would rise 2% to 4% for the quarter.

On Thursday, JetBlue said that RASM had increased approximately 3.1% in the second quarter, slightly better than the midpoint of its revised forecast. The company did not provide an update to its cost outlook.

A JetBlue Airways plane preparing to land

JetBlue's Q2 RASM growth was in line with the airline's most recent forecast. Image source: JetBlue Airways.

That said, there are some reasons for optimism about JetBlue's cost performance. First, oil prices have declined over the past three months. Thus, JetBlue likely paid less for fuel last quarter than the $2.21 per gallon it had estimated in April, which already would have been lower than its $2.28-per-gallon average price in the prior-year period. JetBlue's initial guidance also called for a modest year-over-year improvement in fuel efficiency.

Second, the carrier had another quarter of solid operational performance. JetBlue completed about 99.3% of its scheduled flights last quarter, easily beating its Q2 2018 performance, especially in May and June. This uptick in completion factor may have allowed JetBlue to limit its nonfuel unit cost growth to the lower end of its guidance range for a 1.5% to 3.5% increase.

The combination of a solid RASM increase, modest nonfuel unit cost growth, and lower fuel costs should put JetBlue on track to post strong earnings for the second quarter. Analysts currently expect adjusted earnings per share to surge 47% year over year to $0.56.

Spirit Airlines also stands pat

Spirit Airlines provided a more comprehensive investor update on Thursday. The budget carrier said that RASM rose approximately 5% last quarter, while nonfuel unit costs increased 4.6%. Both metrics were exactly in line with the guidance that Spirit had provided in April.

A yellow Spirit Airlines jet parked at an airport gate

Spirit Airlines' unit revenue and nonfuel unit costs matched its April guidance. Image source: Spirit Airlines.

Of course, Spirit Airlines also benefited from lower-than-expected fuel costs last quarter. The carrier paid an average of $2.16 per gallon for jet fuel, down from its initial estimate of $2.25 per gallon and well below the $2.32 per gallon it paid during the second quarter of 2018.

Based on this revised fuel cost forecast and the other elements of Spirit's guidance, the budget carrier is likely to report adjusted EPS of approximately $1.65 for the second quarter. That would be up 49% from $1.11 in the year-ago period and slightly ahead of the average analyst estimate of $1.62.

Plenty of earnings growth to look forward to

Obviously, JetBlue and Spirit Airlines can't continue to grow EPS at a nearly 50% year-over-year pace indefinitely. Nevertheless, both companies have ample earnings growth opportunities.

In the near term, the 737 MAX grounding could have an even bigger impact on industry capacity growth in the second half of 2019 than it did last quarter. This should support solid unit revenue trends for JetBlue and Spirit in the third and fourth quarters.

Looking ahead to 2020, JetBlue is primed for margin expansion as the carrier introduces basic economy pricing and its cost-cutting plans start to pay off in a big way. Meanwhile, Spirit Airlines will continue expanding at a double-digit rate and could start to benefit from an updated loyalty program and an increase in the number of connecting route opportunities.

Shares of both airlines currently trade for less than 10 times their estimated 2019 earnings. At these bargain prices, JetBlue Airways stock and Spirit Airlines stock look extremely attractive for long-term investors.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.