Arrange Flex sdk with air 33

Since there is no a ready-to-use solution to compile Flex with Air 33, you need to arrange flex sdk with the latest version of Air that supports the compiling for arm 64bit.
Download flex sdk binaries from Apache Flex and the air sdk from Harman.
Overlay air into flex folder just donwloaded, using this command:
cp -rf airSdkFolder/* yourFlexSdkFolder
Remove all {airHome} references from frameworks/airmobile-config.xml, and leave the correct relative path.

Generating apk

If the generation of the apk works properly with Flash Builder, you have only to select the architecture you want to use.
To specify the compiling for 64 bit architecture, go to lib/adt.cfg of your flex sdk folder and uncommenting the lines:
#DefaultArch=armv8
#OverrideArch=armv8

Since this way was not working in my experience, I chose to generate the apk by command line.
Compile the project from Flash Builder (Export release build), this operation will generate a swf file.
Duplicate the sdk folder wherever you want (just not to spoil the original sdk folder).

In this folder, under  /bin folder, move your yourproject-app.xml file and yourApp.swf (just generated).
Probably you need also to move some graphic resources (in my case are all included in a folder called assets).

Run:
./adt -package -target apk-captive-runtime -arch armv8 -storetype pkcs12 -keystore yourCertificate.p12 yourApp.apk yourproject-app.xml yourApp.swf assets/*

This command will create a .apk file signed with the certficate you chose and for the architecture you specified (armv8 in this case).