This is an extract from an NTSB report involving a PA31 where the aircraft could not maintain altitude in the US; OAT 40 degrees C at 2000 elevation.
Based on both the pilot's report of the conditions at the landing site and the METAR from the closest aviation observation station, the density altitude on the surface was calculated to be 4,700 feet. The outside air temperature at the site, and the estimated temperature at the aircraft's cruise altitude, were outside of the temperature envelope for a positive rate of climb on the aircraft's single engine climb performance chart in the Airplane Flight Manual. According to Piper, the temperature lines on the charts are limits and no extrapolation can be made for points outside of the temperature lines.
Lines in the POH/VG supplement end at 36C at sea level at 1789 amsl the lines extend to just over 34C.
Operating at 40C will lead eventually to an accident report statement as follows;
The fatigue fracture and separation of the No. 6 cylinder fuel injector line due to the company maintenance personnel's failure to comply with an Airworthiness Directive. A factor in the accident was the company's decision to operate the aircraft in environmental conditions, which were outside of the single engine performance capability of the aircraft.
Unless of course there is an updated set of charts.
Report date was July 23 2000 rego N600EE