Two months ago, Spirit Airlines (SAVE 0.36%) reported stellar results for the fourth quarter of 2018, including an 89% surge in adjusted earnings per share. At the time, it projected that this incredible earnings momentum would continue in the first quarter of 2019.

On Wednesday afternoon, Spirit modestly reduced its Q1 outlook. However, its guidance cut was quite mild relative to those made since early March by rival leisure airlines, including JetBlue Airways (JBLU -0.66%). Moreover, Spirit Airlines remains on track to post extraordinary EPS growth for the recently ended quarter.

Spirit's stellar forecast comes down a bit

Back in February, Spirit Airlines projected that revenue per available seat mile (RASM) would rise 5% in the first quarter on 16.5% capacity growth. The carrier estimated that its adjusted nonfuel unit costs would increase by a comparatively modest 2% to 3% year over year. Furthermore, Spirit expected lower fuel costs -- averaging $2.06 per gallon, compared to $2.15 per gallon a year earlier -- to offset most of that cost creep.

This outlook implied that EPS would roughly double year over year in the first quarter. Indeed, as of Wednesday, the average analyst estimate called for first-quarter EPS of $0.87, compared to $0.44 in Q1 2018.

However, Spirit's guidance update this week indicated that RASM rose about 4% last quarter: 1 percentage point less than its prior forecast. The carrier attributed this reduced unit revenue outlook to lower-than-expected fares in March and capacity growth coming in slightly above expectations. Not much changed on the cost side. Nonfuel unit costs were in line with Spirit's initial guidance, and while fuel prices averaged $2.09 per gallon (a little more than the airline had projected), Spirit exceeded its target for fuel efficiency.

A yellow Spirit Airlines jet parked at an airport gate

Spirit Airlines trimmed its Q1 forecast on Wednesday, but not by much. Image source: Spirit Airlines.

The net result is that Spirit Airlines will likely fall short of the current analyst EPS consensus for Q1 by a few pennies. Yet this still implies that EPS nearly doubled year over year.

The damage was much worse at JetBlue

Spirit Airlines is just the latest leisure-focused airline to cut its first-quarter outlook. Given how badly many of its peers missed their forecasts, investors should be pretty happy about Spirit's recent guidance update.

For example, JetBlue Airways reduced the midpoint of its Q1 RASM forecast by 2 percentage points last month. That stung especially hard because its original guidance called for a 0.5% RASM decline at the midpoint of the range.

On Wednesday, JetBlue updated investors again, stating that RASM fell about 3.1% in the first quarter. That was near the bottom of the revised guidance range it had provided in March, due to higher-than-planned capacity. JetBlue and Spirit Airlines have a meaningful level of route network overlap -- particularly in Fort Lauderdale and Orlando -- so it's encouraging that Spirit Airlines achieved dramatically superior revenue results last quarter.

The second quarter could be even better

Spirit Airlines faced a significant revenue headwind in the first quarter from Easter shifting into late April this year. The Easter shift will become a big tailwind in the second quarter.

Furthermore, the grounding of the Boeing 737 MAX has forced several of the top U.S. airlines -- and especially Southwest Airlines -- to trim their schedules for the next few months. That artificial capacity constraint could help Spirit Airlines (which only operates Airbus A320-family planes) capture additional traffic and higher fares this quarter.

As a result, Spirit Airlines could potentially post even stronger EPS growth in Q2 than it did in each of the last two quarters. With that kind of outlook, investors shouldn't worry about the modest reduction in the carrier's first-quarter forecast.