To roughly clarify without looking anything up, the IRS 415c limit is $52000 for the retirement plan. If you are over 50, you can add a $5000 catch up contribution to that for a total of $57k (this extra $5k isn't accounted for in the explanation below).

Your personal pretax limit on what you can contribute is $17500 towards the $52k limit...
DAL does a 15% contribution which is separate and independent of what you contribute...except the grand total of yours and theirs has to come in under the 415c limit of $52k.

If you do the math, to max out your 401 to the 415c limit, you would make your full 17500 contribution and the company would max out their share ($34500) if you made more than $230k+/-

That is about as simplified as I can get...there are other issues if you make more, but in those cases, you should max out your pretax contribution earlier in the year.