I have a couple of questions about CAT A procedures for the AW139. For reference I am looking at RFM
Supplement 12 Cat A operations,
Supplement 50 6800kg and
Supplement 68 Phase 5 additional functions.
According to supplement 12
"For a Ground Level or Elevated Heliport/Helideck, without obstacles in the
take off flight path, the Vertical procedure with TDP fixed at 35ft can be used."
Nowhere does it say anything about a 20ft TDP option for the Elevated Helideck portion in supp 12. However in supplement 68 it talks about the CAT A takeoff symbology for ELEV HELIPAD which gives a 20ft TDP as default. It would be easy to assume that this option is for the Offshore Helideck Procedure, which uses a 20ft TDP, but the procedure for that in Supp 12 clearly states that a variable PI target should be used taken from the graph given. Therefore the symbology cannot be used as this gives a flat hover PI plus 23% at all hover PI's.
The caution below in supplement 68 comes with no reference and I was wondering if anyone knows more details for its meaning if there is no profile given for a 20ft TDP (except the offshore helideck)
Take-Off Symbology - Vertical Profile
The Take-Off profiles indicated on the PFD are to be used with the fol-lowing Supplement 12 CAT A Operation PARTs:
— HELIPAD - PART A - Ground Level and Elevated Heli-port/Helideck Vertical Take Off Procedure
— SHORT FIELD - PART B - Shortf Field Take Off Procedures
— ELEV HELIPAD - PART A - Ground Level and Elevated Heli port/Helideck Vertical Take Off Procedure
— BKUP HELIPAD - PART C Ground Level and Elevated Heliport/ Helideck Back-Up Procedure
When on the ground after selection of any vertical Take-Off profile the TDP height magenta bug is presented on the Rad Alt tape at the default value of 35 ft (85 ft for BKUP HELIPAD). This value should be modified, as required, for the profile being carried out using the DH rotary knob.
CAUTION
The ELEV HELIPAD displays a default TDP value of 20 ft which is lower than the PART A - Ground Level and Elevated Heliport/ Helideck Vertical Take Off Procedure TDP minimum so requires adjustment.
I'd like to know if anyone knows the correct use for the ELEV HELIPAD 20ft TDP symbology. It would be logical to me to say that it is intended for the Ground Level or Elevated Heliport/Helideck procedure when the elevation of the Heliport/Helideck is at least 15ft above the ground. But this is not mentioned in the RFM as far as I can see.
Thanks for your help.