fixed a typo

apps/systemlib/airspeed.c

@@ -87,7 +87,7 @@ float calc_true_airspeed_from_indicated(float speed_indicated, float pressure_am
  *
  * Note that the true airspeed is NOT the groundspeed, because of the effects of wind
  *
- * @param total_pressure pressure inside the pitot/prandl tube
+ * @param total_pressure pressure inside the pitot/prandtl tube
  * @param static_pressure pressure at the side of the tube/airplane
  * @param temperature_celsius air temperature in degrees celcius
  * @return true airspeed in m/s

apps/systemlib/airspeed.h

@@ -78,7 +78,7 @@
   *
   * Note that the true airspeed is NOT the groundspeed, because of the effects of wind
   *
-  * @param total_pressure pressure inside the pitot/prandl tube
+  * @param total_pressure pressure inside the pitot/prandtl tube
   * @param static_pressure pressure at the side of the tube/airplane
   * @param temperature_celsius air temperature in degrees celcius
   * @return true airspeed in m/s