I just tried 3 sd cards which all work fine on the mavic pro and phantom 4 but I'm getting "sd card error" on the mavic air. I cant get any sd cards to work on it, only the internal memory. wont even let me format it.

It is simple. P4 and Mavic Pro write "only" with max 60 Mb/s for your SD card while Mavic Air writes at 100 Mb/s. Therefore, you must purchase a new SD card that can match the requirements of Mavic Air's camera.

Borrowed from Mavic Air FAQ:  https://www.dji.com/mavic-air/info#specs

SD Card Capacity        Class/UHS

16 GB        Sandisk Extreme; Kingston SDHC-I SDCAC/16GB
32 GB        Sandisk Extreme V30; Sandisk Extreme V30 A1; Sandisk Extreme V30 Pro A1
64 GB        Sandisk Extreme V30 A1; Sandisk Extreme Pro V30 A1
128 GB        Sandisk Extreme V30 A1; Sandisk Extreme Plus V30 A1

Good luck, regards Leif.

I'm using this.. 128 GB        Sandisk Extreme V30 A1; Sandisk Extreme Plus V30 A1

started working. I updated the FM but then had to update to yet another one once I got home and now it's working fine with all the cards. close call, whew!!

fans589cba4b Posted at 2018-6-10 13:10
started working. I updated the FM but then had to update to yet another one once I got home and now it's working fine with all the cards. close call, whew!!

Glad it worked out.  I suggest doing all of the Calibrations like IMU/Gimbal/RC/VPS/Compass since you have updated the firmware.

I am sorry for the trouble. I understand that you are having issues with the SD card for your Mavic Air. May I know what is the model and class of your SD card. The SD card's compatibility might be the reason why it is working properly. I will be sending the list of recommended SD card for reference.

fans589cba4b Posted at 2018-6-10 13:10
started working. I updated the FM but then had to update to yet another one once I got home and now it's working fine with all the cards. close call, whew!!

Make sure you follow @SparksBird's advice.   It is important to do this.