Erased my Macintosh HD

What version of OS X did you have before erasing? Lion? Did you try recovery mode? I think you hold Option at startup and you can choose to boot from the Recovery HD volume. You should be able to download OS X from there, but not the other data like apps, which shouldn't matter if you are trying to reset to factory.

Assuming that your MBA came with Lion or later, boot the MBA with the OPTION + COMMAND + R keys. This should result in a display with a revolving globe. This will connect you to the Apple servers and allow you to install the ORIGINAL OSX.

http://osxdaily.com/2014/12/14/reinstall-os-x-mac-internet-recovery/

Ciao.

I need specific information regarding your MBP. Find the serial number:

https://support.apple.com/en-us/HT204308

Enter it here and post back the model/year information.

https://selfsolve.apple.com/agreementWarrantyDynamic.do

Ciazo.

A 2010 MBA came with Snow Leopard (10.6) originally. Use the original installation media, erase the HDD and install Snow Leopard. Then install the Snow Leopard combo update:

https://support.apple.com/kb/DL1399?locale=en_US

That will allow you to install any newer OSX (From Lion on up).

Ciao.

Boot the MBP from the Snow Leopard disk.

After the language selection, the display should have a menu bar on top.

Click on UTILITIES.

From the drop down menu, select Disk Utility.

Run Disk Utility>Erase and make certain that the format is Mac OS Extended (Journaled).

Exit Disk Utility and complete the OSX installation.

Ciao.

Duplicate Snow Leopard OSX disks can be ordered from Apple Customer Service. They will require the serial number of your MBA and there is a fee.

Ciao.