Rothschilds' appointment seems sensible. The various Davies reports on financing the new runway capacity have highlighted the fact that the balance sheets of both HAL and GAL would be transformed as a result of investment in a new runway. There would be a serious amount of egg on face if a Govt decision in favour of either airport was followed by a problem with financing.
The Rothschilds input will also be important in the CAA's consideration of how the new runway will affect economic regulation. One of the CAA's duties is to take into account the airports' ability to finance new investment, and they will need to carefully consider whatever Rothschilds say before making any final pronouncements.
Probably the most interesting aspect will be Rothschilds' view on Gatwick. In particular, GAL are proposing a doubling of airport charges in the face of no airline support, a generally-held view (including by CAA) that GAL's current charges are close to market clearing levels, and a gradual deregulation by CAA of GAL's airport charges. Quite how GAL could raise new debt to fund R2 in these circumstances is beyond me, and it is entirely possible that Rothschilds will conclude that the Gatwick R2 project is simply not fundable without public sector support. That would be interesting.