Thank you all for your comments.
Found this
http://www.flightglobal.com/pdfarchi...0-%201470.html but it is 1949. Whitley spec was 1934. I did find an ARC or RAE article, but cannot find it now.
The Captain and crew of a Whitley V survived a forced landing when their tail beam (beam which also holds the rear wheel) failed at the end of July 1940 and within two weeks another occurred at Boscombe Down. By December 1940 a modified tail beam kit had been designed by AW and was being supplied to 4 Group and Contractors. Any weakness appeared to be in the tail.
Later in WW2 a second Whitley tail beam modification was supplied to supersede the first modified Dec 1940 tail beam.
Mark