The short version is:  You can't use the PerDiem deduction for 2018 on your Federal taxes, but you might be able to for your state taxes.  

Here's the long version:

Beginning in tax year 2018 you will no longer be allowed to claim a meal allowance while traveling as an airline crew member on your tax return due to changes in the tax law passed by congress in the Tax Cuts and Jobs Act of 2018 (TCJA). The TCJA eliminated the deduction for employee business expenses for W-2 employees that were reported on Form 2106. Therefore, you will not need a PerDiemMax report for your 2018 federal tax return. If you or your accountant have further questions please contact and they will provide you further technical guidance.

Please do not purchase a 2018 PerDiemMax Tax report for 2018 federal tax returns, 2018 Tax Reports are now available for use on certain state income tax returns. Due to changes in federal tax law, per diem reports are not beneficial for 2018 federal tax returns, you may still use them on 2017 and earlier federal tax returns. You may benefit from the PerDiemMax Tax Report for 2018 state income tax returns for California, Alabama, Arkansas, Hawaii, Iowa, Minnesota, New York and possibly others; check with your accountant for details.