What does "a flight to quality" mean?

I was reading an article on the Economist about revolutionizing management education and came across an interesting expression.

Geoffrey Garrett, dean of the Wharton School, at the University of Pennsylvania, believes that a flight to quality is benefiting top institutions like his - and their graduates.

Here is the context: The previous paragraphs talk about how improved schools outside the U.S. are allowing foreign students to study closer to home. Also, MBA programs have become less popular among U.S. students.

What does "flight" mean in the sentence? Is "a flight to sth" a set phrase?

It‘s a double entendre, so two meanings at once.

"Flight" as to flee

As user067351 says, the statement is borrowing a term-of-art (insider jargon) from the financial industry:

A flight-to-quality, or flight-to-safety, is a financial market phenomenon occurring when investors sell what they perceive to be higher-risk investments and purchase safer investments, such as US treasuries or gold. (Wikipedia)

The literal expression means fleeing high-growth but high-risk investments due to an expected downturn in which the risk will exceed the growth, so selling them high and moving into safer investments like bonds.

The speaker is saying that US MBA programs are the best, and despite improvement in foreign school programs, foreign students still feel safer investing their time and tuition in the best.

"Flight" as desirable transportation mode, esp. across seas

And "quality" as the speaker's own institution :)

The metaphor is that the foreign students are "flying" (to cross the ocean) to a "quality" university.

This is why the speaker selected "flight to quality" instead of "flight to safety" above. The latter make it sound like they are refugees, whereas the former allows the speaker to brag.

Garrett is using a very common idiomatic expression from the financial world:

A flight-to-quality, or flight-to-safety, is a financial market phenomenon occurring when investors sell what they perceive to be higher-risk investments and purchase safer investments, such as US treasuries or gold.

(Wikipedia)

By analogy, he thinks that students moving away from lower-quality schools will benefit higher-quality ones.

In this case, it's meaning flight as in "the act of fleeing or running away, as from danger", to quote a definition from thefreedictionary.com. The article is saying that graduates are running away from lower-quality institutions towards higher-quality institutions.