Across the country, big jets are disappearing -- nudged shoved aside by the little guys, which are cheaper to operate and don't require as many butts to fill seats.

The number of empty seats falls, and revenue per available seat-mile (RASM) goes up. It's pretty straightforward. But, for crowded flights, this could leave a few people stuck without their preferred routes. The alternative, of course, is an unsustainable status quo, in which a few passengers remain happy ... until the airline folds.

What's one over-the-horizon trend that passengers (and investors) would be wise to monitor closely? Micro airlines.

Micro airlines will be small carriers that target the leisure travel market, stock analyst and frequent flier C. Leonard Bauer told BloggingStocks Tuesday.

Bauer is quick to point out that these carriers don't exist today -- the commercial aviation sector's financials can't currently support them -- but when design advances (including composites), increased engine efficiency, and a drop in oil and aviation fuel prices turn in the airline sector's favor, look for micro carriers to sprout, he predicted.

A streamlined air itinerary

Further, Bauer doesn't count current 'regional airlines' or 'express airlines' such as United Express as micro airlines because micro airlines will differ from the former in one significant way: "They'll have vastly reduced check-in times compared to regional airlines," Bauer said. "For a portion of the leisure travel public, this will be the deal-clincher." Bauer added that he doesn't own shares in nor have a rating on any airline.

Delta Air Lines (NYSE: DAL) Monday said it is continuing to review strategic options and that it did not expect an "immediate" sale of its regional jet service Comair, Reuters reported.

Delta's shares fell 21 cents to $13.18 in mid-day Monday trading.

Delta (NYSE: DAL) has considered a sale of Comair since exiting bankruptcy in April 2007. Along with a company restructuring and an evaluation of Comair's operation, Delta is exploring strategic options, including joint ventures or mergers.

Last fall, Delta and United Airlines (NASDAQ: UAUA) denied that they had held merger talks after a hedge fund Paradus Capital Management LP recommended that they merge.

Last December, over 100 stocks were featured in our Top Picks for 2007 report. Now, at mid-year, we turn to the 20 advisors whose picks showed the strongest gains to get an update on their previous picks, as well as a new favorite stock for the second half of the year.

David Fried, editor of the Buyback Letter, chose Big Lots Inc. (NYSE: BIG) as his favorite stock for 2007, which rose 39% as of 6/1/07. Please see his original recommendation and his current opinion on Big Lots.

Fried's new pick is SkyWest, Inc. (NASDAQ: SKYW). He explains, "SkyWest, the nation's largest independently owned regional airline, is a contract carrier for United Airlines, Delta Air Lines and, most recently, Midwest Airlines.

"Nimbler than the big legacy carriers and not burdened by their bloated labor costs, SkyWest has a steady earnings stream, good cash flow, and an attractive P/E of 11. Its reputation as an efficient, low-cost operator and as the best-managed regional airline in the business was enhanced with the 2005 acquisition of Atlantic Southeast Airlines, which made SkyWest a player on the national stage.

"Since the mid-1970s, SkyWest has grown from a company with annual revenue of under $1 million to a publicly held company with annual revenues of more than $1 billion and almost 15,000 employees. SkyWest is set for continued long-term growth.