While the proven Zacks Rank places an emphasis on earnings estimates and estimate revisions to find strong stocks, we also know that investors tend to develop their own individual strategies. With this in mind, we are always looking at value, growth, and momentum trends to discover great companies.

Considering these trends, value investing is clearly one of the most preferred ways to find strong stocks in any type of market. Value investors use fundamental analysis and traditional valuation metrics to find stocks that they believe are being undervalued by the market at large.

Zacks has developed the innovative Style Scores system to highlight stocks with specific traits. For example, value investors will be interested in stocks with great grades in the "Value" category. When paired with a high Zacks Rank, "A" grades in the Value category are among the strongest value stocks on the market today.

One stock to keep an eye on is American Airlines (AAL). AAL is currently sporting a Zacks Rank of #2 (Buy), as well as a Value grade of A. The stock has a Forward P/E ratio of 6.04. This compares to its industry's average Forward P/E of 15.67. Over the past year, AAL's Forward P/E has been as high as 10.54 and as low as 4.01, with a median of 6.43.

Finally, our model also underscores that AAL has a P/CF ratio of 3.57. This metric takes into account a company's operating cash flow and can be used to find stocks that are undervalued based on their solid cash outlook. AAL's P/CF compares to its industry's average P/CF of 11.40. AAL's P/CF has been as high as 4.58 and as low as 2.65, with a median of 3.51, all within the past year.

Frontier Group (ULCC) may be another strong Transportation - Airline stock to add to your shortlist. ULCC is a # 2 (Buy) stock with a Value grade of A.

Frontier Group is currently trading with a Forward P/E ratio of 8.98 while its PEG ratio sits at 0.23. Both of the company's metrics compare favorably to its industry's average P/E of 15.67 and average PEG ratio of 0.74.

ULCC's Forward P/E has been as high as 148.72 and as low as 4.55, with a median of 11.68. During the same time period, its PEG ratio has been as high as 0.25, as low as 0.21, with a median of 0.22.

Frontier Group sports a P/B ratio of 2.96 as well; this compares to its industry's price-to-book ratio of 4.88. In the past 52 weeks, ULCC's P/B has been as high as 3.75, as low as 1.22, with a median of 2.64.

Value investors will likely look at more than just these metrics, but the above data helps show that American Airlines and Frontier Group are likely undervalued currently. And when considering the strength of its earnings outlook, AAL and ULCC sticks out as one of the market's strongest value stocks.

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American Airlines Group Inc. (AAL) : Free Stock Analysis Report

Frontier Group Holdings, Inc. (ULCC) : Free Stock Analysis Report

This article originally published on Zacks Investment Research (zacks.com).

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