Climb performance calculation

[ustyva 9]

Hello all! I have a question about the climb performance calculation with the 737. Last week I made 2 different flights, one departing from LOWI and one from LFMN. Both require a climb gradient, LOWI RATT2J departure has a required climb gradient of 4,7% due to a cumulus granitus in the takeoff sector :) It is located at 17 NM after DER (18,2NM after brake release) and 4700ft-AAL (6700AMSL) For LOWI I used the PMDG FCOM1 PD.30.9 (page 366) Takeoff obstacle limit weight. This table only counts for obstacles up to 300m and 9km from brake release so I am not sure this is the correct table to use, but because I cannot find any other, I used it be calculating a fictional obstacle of at 6km and that would be 282 meters high. With these figures I went into the tables and find:58.4t reference obstacle limit weightno OAT adjustment required-4.3t pressure altitude adjustment5kt hw correction = +0,4tPacks OFF +0.6t Climb Performance limited weight of: 55.1t This sounds pretty reasonable. In the FMS I typed thrust reduction altitude 4500AGL and acceleration and EO acceleration altitude 7500 (due to a second 3.3% sid part up to 9500) I am pretty sure these figures are based on an engine failure after V1. when I flew the departure with 2 engines on, I had a way better climb performance. Now to France, LFMN has a minimum climb gradient of 7% (!) up to FL100 for ATC reasons. If I use the same way of calculating I end up with a 280m obstacle at 4km.this would give me: 48.6t reference obstacle limit weightno OAT adjustment requiredno pressure altitude adjustmentno hw correctionPacks OFF +0.6t Climb Performance limited weight of: 49.2t But the major difference with Innsbruck is: In Nice, there is no actual obstacle. If I have an engine failure after v1, I would accelerate over the Mediterranean sea, inform ATC request vectors for landing. The 49.2 t restriction is too limiting. The climb limit weight in table PD.30.2 (page 360) is based on the normal 3.3% climb gradient so I cannot use it. On page PD.32.6 I found another climb gradient table, but it is only for flaps 15 and used for GA thrust. For Nice I skipped the climb limiting performance calculation, used no de-rate and no assumed temperature and I made it!But next time I would like to correctly calculate rather then try and hope. Any help would be welcome! :)

[badderjet 174]

Wow why I can't exactly help you with your issue I'd certainly like to get an answer as well. Your method sounds reasonable even if it's "abusing" the chart a little bit. I see no other chart that deals with gradients except for the one with go arounds.