Method and system for determining friction coefficient μ for an aircraft landing event

1. A method of determining a ground-to-tyre friction coefficient for an aircraft landing event of an aircraft landing gear, the method comprising:

providing a plurality of aircraft data parameters including a provided aircraft vertical acceleration to an aircraft computational model and repeatedly modelling the aircraft landing event using the aircraft computational model by varying one or more initial conditions of the aircraft computational model until a best match between a modelled value of aircraft vertical acceleration and the provided aircraft vertical acceleration is determined;

providing the aircraft computational model initial conditions associated with the best match of modelled and provided aircraft vertical acceleration values to a landing gear computational model and also providing a measured strain value derived from a first sensor located on the aircraft landing gear to the landing gear computational model, the landing gear computational model having a value for the ground-to-tyre friction coefficient as a variable condition;

modelling the aircraft landing gear to generate a modelled strain value and comparing the modelled strain value with the measured strain value;

repeating the landing gear modelling step with a different value for the ground-to-tyre friction coefficient until a best match between the modelled strain value and the measured strain value is determined and outputting the respective friction coefficient value; and

analysing an output of the landing gear computational model for the determined ground-to-tyre friction coefficient to determine if a landing gear overload occurred during the aircraft landing event.

2. The method of claim 1 , wherein at least a portion of the aircraft data parameters are provided by an aircraft flight data recorder.

3. The method of claim 2 , wherein a further portion of the aircraft data parameters are provided by at least one remote inertial measurement unit located on the landing gear of the aircraft.

4. The method of claim 3 , wherein the at least one remote inertial measurement unit samples the aircraft data parameters at a frequency greater than 8 Hz.

5. The method of claim 1 , wherein a further input is provided to the aircraft computational model, the further input being provided by a second sensor located on the aircraft landing gear and arranged to measure a further one of the values modelled by the aircraft computational model other than the aircraft vertical acceleration and wherein the aircraft landing event is repeatedly modelled until a best match of the modelled and measured further values is additionally determined.

6. The method of claim 5 , wherein the further value comprises a shock absorber travel of the landing gear.

7. The method of claim 1 , wherein the strain value is indicative of a drag loading of the landing gear.

8. The method of claim 7 , wherein the first sensor comprises a strain gauge located on a drag stay on the landing gear.

9. A system for determining a ground-to-tyre friction coefficient for an aircraft landing event of an aircraft landing gear, the system comprising:

a flight data acquisition system arranged to record a plurality of aircraft data parameters including an acquired aircraft vertical acceleration during the aircraft landing event;

an aircraft computational model arranged to receive the plurality of aircraft data parameters and to repeatedly model the aircraft landing event by varying one or more initial conditions until a best match between a modelled value of aircraft vertical acceleration and the acquired value of aircraft vertical acceleration is determined;

a first sensor located on the aircraft landing gear arranged to generate a measured strain value during the aircraft landing event;

a landing gear computational model having a value for the ground-to-tyre friction coefficient as a variable condition and arranged to:

receive the aircraft computational model initial conditions associated with the best match of modelled and acquired aircraft vertical acceleration values;

receive the measured strain value from the first sensor;

model the landing gear to generate a modelled strain value and compare the modelled strain value with the measured strain value; and

repeat the modelling step with a different value for the ground-to-tyre friction coefficient until a best match between the modelled strain value and the measured strain value is determined and outputting the respective friction coefficient value; and

an analysis module to analyse an output of the landing gear computational model for the determined ground-to-tyre friction coefficient to determine if a landing gear overload occurred during the aircraft landing event.

10. The system of claim 9 , wherein flight data acquisition system comprises an aircraft flight data recorder.

11. The system of claim 10 , wherein the flight data acquisition system further comprises at least one remote inertial measurement unit located on the landing gear of the aircraft.

12. The system of claim 11 , wherein the at least one remote inertial measurement unit samples the aircraft data parameters at a frequency greater than 8 Hz.

13. The system of claim 9 , further comprising a second sensor located on the aircraft landing gear arranged to measure a further one of the values modelled by the aircraft computational model other than the aircraft vertical acceleration and wherein the aircraft computational model is further arranged to receive an output from the second sensor and repeatedly model the aircraft landing event until a best match of the modelled and measured further values is additionally determined.

14. The system of claim 13 , wherein the second sensor is arranged to measure a shock absorber travel of the landing gear.

15. The system of claim 9 , wherein the strain value is indicative of a drag loading of the landing gear.

16. The system of claim 15 , wherein the first sensor comprises a strain gauge located on a drag stay on the landing gear.