Compiling Flex Air apps for PC, Android and Mac from one codebase?

I would like to use Air to build for PC, Mac, Android, Ios.

Is it possible to do this from a single code base as Adobe Suggests.

Or will I need to maintain 4 separate builds?

Some guidance would be appreciated.

I have been able to maintain a single code base to date. I have done things like the following:

        private function getHostName() : void
        {
            if (NativeProcess.isSupported)
            {
                var OS : String = Capabilities.os.toLocaleLowerCase();
                var file : File;

                if (OS.indexOf('win') > -1)
                {
                    // Executable in windows
                    file = new File('C:\\Windows\\System32\\hostname.exe');
                }
                else if (OS.indexOf('mac') > -1 )
                {
                    // Executable in mac
                }
                else if (OS.indexOf('linux'))
                {
                    // Executable in linux
                }

                var nativeProcessStartupInfo : NativeProcessStartupInfo = new NativeProcessStartupInfo();
                nativeProcessStartupInfo.executable = file;

                var process : NativeProcess = new NativeProcess();
                process.addEventListener(NativeProcessExitEvent.EXIT, onExitError);
                process.addEventListener(ProgressEvent.STANDARD_OUTPUT_DATA, onOutput);
                process.start(nativeProcessStartupInfo);
                process.closeInput();
            }
        }

        private function onOutput(event : ProgressEvent) : void
        {
            var strHelper : StringHelper = new StringHelper();
            formStationID.text = event.target.standardOutput.readUTFBytes(event.target.standardOutput.bytesAvailable);
            formStationID.text = strHelper.trimBack(formStationID.text, "\n");
            formStationID.text = strHelper.trimBack(formStationID.text, "\r");
        }

        private function onExitError(event : NativeProcessExitEvent) : void
        {
        }

To take care of native calls. Other than the native calls I have found few things that can't be written generically, but of those, the above approach should work with any part of the code set as well.