Actually, to be pedantic, the run dry test that AW does is done with the MGB totally drained of oil. No back up system. The back up system is only for Oil and Gas machines and is a very recent add-on with the 139 (copied from 189 system).
The 139 MGB was run for 30 minutes with oil, then drained of oil and run a further 30 minutes. Freewheels were then pulled to see how much damage was done. Freewheels were then put back and a FURTHER 30 minutes dry running was done (all at 100% NR and 100%TQ).
MGB was then stopped and inspected again. Inputs were toast. Paint was all brown and bubbling off. Smoke everywhere.
If you want to have a look at that MGB, go to Sesto, it is on the Maintenance Sim. Every mechanic who does the practical training there pulls the freewheel out and inspects it. Jaws often drop
169 MGB ran continuously for 52 minutes dry (no back up system) before they stopped the test.