This is an example of the messages from the sensor when you use SENSOR_SYNC_SEND-
35.958 7 BMP_STATUS 349718 25970 99597 222
36.021 7 AIRSPEED_ETS 1576 1573 3.863097
36.041 7 ATTITUDE 0.007594 3.089026 0.008883
36.047 7 GPS 0 61869336 669580224 0 75816 0 0 1740 58323250 31 3
36.051 7 SVINFO 3 4 12 6 30 26 70
36.055 7 ALIVE 33,225,105,215,49,236,3,215,91,28,20,90,106,188,171,253
36.075 7 NAVIGATION 0 2 10.4 -5. 0. 132.6 0 0
36.122 7 AIRSPEED_ETS 1576 1573 3.772374
36.143 7 ATTITUDE 0.007577 3.089344 0.008838
36.150 7 DESIRED 0. 0. 0. 0. 0. 120. 0. 15.
36.152 7 ESTIMATOR 75.81601 2e-06
36.156 7 IMU_GYRO 0.008301 0.013184 -0.003418
36.158 7 PPRZ_MODE 0 0 0 0 0 17
36.174 7 BMP_STATUS 349679 25969 99583 222
36.221 7 AIRSPEED_ETS 1576 1573 3.681651
36.242 7 ATTITUDE 0.007621 3.089588 0.008804
So AIRSPEED_ETS is sent many times each second. Normally you should get immediate response when blowing into the sensor.
Maybe a logic analyzer would be the next thing to use to check that the values really change on the I2C bus when you blow into the sensor,
Helge.