A tax bracket determines the tax rate for the level of income you find yourself at.  Tax brackets are often misunderstood.  Many people mistakenly think that if you hit a higher tax bracket, that all of your income is subject to the tax rate of the higher tax bracket.  That is not how it works.

Rather, the tax rate that you see for your own taxes are taxed at different tax brackets up to your income level.  For example, assume that there are 4 tax brackets that exist.  Assume:

tax bracket 1: 15% ($0 - $19,999)
tax bracket 2: 25% ($20,000 - $49,999)
tax bracket 3: 35% ($50,000 - $99,000)
tax bracket 4: 45% ($100,000 +)

In this simple example, assume you make $150,000.  That does not mean your entire income is taxed at 45%, which would be $67,500.  Instead, it is taxed in tiers, so your $150,000 income is taxed as follows:

tier 1:  $19,999 x .15% = $3,000
tier 2:  ($49,999 - $19,999) x .25% = $7,500
tier 3:  ($99,999 - $49,999) x .35% = $17,500
tier 4:  ($150,000 - $99,999) x .45% = $22,500

$3,000 + $7,500 + $17,500 +$22,500 = $50,500

In this example, the $150,000 income would lead to a tax of $50,500 (not $67,500).  The effective tax rate in this example is ($50,500/$150,000) = 33.67%, which is considerably lower than the tax bracket.  This means that the effective tax rate is always lower than the flight crewmember's tax bracket.