Can I fly to Germany with a Travel Decument Form i-327 without visa?

The European Union keeps a spreadsheet of recognised travel documents which entitles the holder to cross the external borders and which may be endorsed with a visa. Here's the relevant section:

As you can see, you can -- and as we will see, you actually need to -- use this document to apply for a visa to Germany.

To answer whether you need a visa, check the German Missions in the United States Visa: Frequently Asked Questions page:

Holders of the “Refugee Travel Document” (Form I-571) which is issued by the United States Department of Homeland Security (DHS) are not required to obtain a visa to enter the Federal Republic of Germany for purposes of business, tourism, or to visit friends if they stay no longer than 90 days. The Travel Document must be valid for at least four months after entering Germany.

Please be advised that this regulation applies to Germany only. If you plan to transit or travel to other Schengen countries you have to contact the responsible consular mission of the respective countries to find out about their visa regulations. Please also note that holders of the very similar document called “Permit to Re-Enter” (Form I-327) do not fall under this rule. Holders of a “Permit to Re-Enter” must apply for a visa.

If you are in doubt whether you are a holder of a “Permit to Re-Enter” or a “Refugee Travel Document” please refer to the data page of the document in your possession issued by DHS. More information on the type of document issued to you can be found above and below the photo in your document.

Emphasis mine. Two more notes:

1. The I-571 document mentioned here gives you significantly more freedom of movement -- you wouldn't need a visa with that one. If you are eligible for it, you should get it.
2. Malta and Denmark won't recognize your document at all and Spain only recognises it for transit or exit to return to the United States. This could be relevant for example if you would attempt to fly Norwegian Airlines via Copenhagen -- that won't work. But, again, if you had an I-571, this wouldn't be a problem.