Loss Of
Control In-flight (LOC-I) is the most frequent cause of General Aviation
accidents and incidents. The proposed concept aims at preventing the risk of
occurrence of a LOC-I by providing an indication of the current margins to
aerodynamic stall conditions, the most frequent cause of LOC-I. Such
indication is based on a derived aircraft angle of attack (AoA) computation
and is shown to the pilot by means of a graphical interface integrated into the
Primary Flight Display or the Multi-functional Flight Display. A colored
vertical bar is used with two indicators that represent AoA with flaps up and
flaps down configurations, in order to show instantly the energy state of the
airplane in either configuration and to enable the pilot to see the available
lift before changing the configuration (crucial when making a go-around).
The
key innovation of the system is that it is simply a software upgrade, not
requiring any dedicated AoA sensor. That is, it does not use an external
appendage or a measuring system on the outside of the airframe. These have
been demonstrated to be key factors in limiting the adoption of such
instruments by General Aviation pilots. A further innovation, with respect to
other methods for deriving AoA, is that the proposed system does not require
any detailed information of the specific aircraft. It uses several parameters
easily gathered from the Pilot Operating Handbook. Other aircraft specific
information is automatically obtained during a calibration flight of ten
minutes.
The system is comprised of: one time entry of various parameters from
the Pilot’s Operating Handbook; one time calibration of an aerodynamic model
of the aircraft, performed during a calibration flight; an algorithm utilizing
an Extended Kalman Filter that merges sensor data (accelerations, velocities,
turn rates, attitude, airspeed) with the calibrated aerodynamic model to
determine the derived aircraft AoA; display of the derived aircraft AoA with
specific ranges that indicate Safe, Caution and Warning regions of AoA; a
monitoring algorithm to check that the system is working properly. The
proposed system has the following unique features: no need of a dedicated AoA
sensor, therefore system accuracy is not dependent upon sensor installation on
the A/C; suitable to be installed on every type of aircraft thanks to the
calibration process; AoA indication based on sensors that have lower noise and
faster response than any other sensor used for AoA direct measurement and are
intended for primary navigation and, as such, are more reliable than direct
AoA sensors; able to detect not nominal working condition that only dedicated
instrumentation could do. In conclusion, the proposed system dramatically
improves general aviation aircraft safety, by providing an immediate,
accurate, and a clear visual display of trend toward stall and stall margin,
without requiring further sensors therefore enabling easy adoption by
everyone. The proposed concept is patent pending and the related commercial
product has been put on the market by Aspen Avionics in July 2015.