This was an unusual departure for TfL; it doesn't normally operate like this. This was a methodical mugging.
It told the Transport Committee of the London Assembly the Aviation Commission's assessment was "substantially underestimating the impact of the third runway".
The criticism went further. TfL says the Aviation Commission did not use the maximum capacity of the runway in its modelling. So instead of 385,000 extra trips per day on the transport network, there could be 450,000.
It said the modelling didn't take into account freight and those trucks would have a huge impact on surrounding roads.
Crucially, the officials also estimated it would cost £15bn to £20bn in investment to build the new rail links required.
And the third runway could create "congestion on road and the rail network and overcrowding on a level we haven't seen".
The sentiments may not be new from TfL; some have implied the officials there are just doing the mayor's bidding - but if they're to be believed. the figures certainly show you the impact a third runway could have on surrounding transport infrastructure.
Update: Heathrow airport has been in touch: "Heathrow's expansion will come with a step-change in rail access to the airport.  With new rail lines to the north, south, east and west, Heathrow can increase the number of passengers taking public transport,  and ensure that even with expansion, there is no more airport-related traffic compared to today.
"We are confident in our plans because we already have an outstanding record in increasing the use of public transport to get to the airport and encouraging people to shift out of their cars. Over the last 20 years, our passenger numbers have risen by almost 80% but airport related traffic has remained static."
Not many were listening or watching, but in City Hall Transport for London (TfL) officials piled into the Aviation Commission's report on Heathrow on Tuesday.