RC_CHANNELS_SCALED/RAW stream from Pixhawk

Hi there,
I’m failing to trigger the transmission of either a RC_CHANNELS_SCALED or _RAW message stream from Px4 in fixed wing configuration.

My setup is a Pixhawk4 mini connected to a Raspberry Pi via serial connection. I already tried it the following two ways:

  1. (void)mavlink_msg_request_data_stream_pack( 1, 1, &message, 1, 0, MAV_DATA_STREAM_RC_CHANNELS, 1, 1 );

  2. (void)mavlink_msg_command_long_pack( 1, 1, &message, 1, MAV_CMD_SET_MESSAGE_INTERVAL, 1, MAVLINK_MSG_ID_RC_CHANNELS_RAW, 1000000, 0, 0, 0, 0, 0 );

Procedure (2) works perfectly for triggering transmission of ACTUATOR_CONTROL_TARGET or GLOBAL_POSITION_INT streams but won’t work RC_CHANNELS_*.

I also attempted to activate transmission from within the NuttX shell using “mavlink stream …” commands. Again works for actuator control target (0) etc. but not for RC channels related streams. Did I miss something essential here?

Grateful for any hints and insight!

Kind regards,