Cant get a class from srvutil

I have a XSD that I need to get a C# class from, I have it on my desktop and I've tried everything to generate a class from it but am getting no where, i've also tried xsd.exe but just get error messages. 

C:\>svcutil.exe /dconly C:\Users\grobinson\Desktop\OTA_AirAvailRQ.xsd /language:C#

C:\>svcutil.exe "C:\Users\grobinson\Desktop\OTA_AirAvailRQ.xsd" /dataContractOnl
y /serializer:DataContractSerializer /language:C# /out:MyDataContract.cs

 The closest I got was using this cmd 

 C:\>svcutil.exe /dconly /importXmlTypes C:\Users\grobinson\Desktop\OTA_AirAvailR
Q.xsd

but I still receive errors like this:-

Error: There was a validation error in the schemas provided for code generation:

    Source:
    Line: 81 Column: 6
   Validation Error: Type 'http://www.opentravel.org/OTA/2003/05/beta:FlightSegm
entType' is no ...