Landing gear monitoring and data analysis help to ensure that this key system continues to function safely during the most difficult phases of a flight. Collins Aerospace’s Michel Babin gives Bernie Baldwin a tutorial on how that challenge is met.
If it wasn’t mission critical, there could be a cogent argument for not having the landing gear on aircraft. It’s very heavy, particularly on long-haul widebody aircraft, and is only in use for a small proportion of the gate-to-gate operation. Not having it on board would reduce aircraft weight and, therefore, emissions and costs considerably.
The reality, of course, is that landing gear is currently the number one viable option for takeoff and landing, so that weight must be hauled around along with the fare-paying passengers and/or cargo. Moreover, the performance of the gear has to be optimal every time, so constant monitoring and care is vital.
When it comes to measuring the performance of the gear, and especially the wheels and brakes, there are key parameters to be monitored. Michel Babin, director, field technical service, landing systems at Collins Aerospace, identifies these, starting with a property intrinsic to a load-bearing mechanical system.
Operational context is key
“We look at the fatigue life over the course of the wheels and brakes system. Collins Aerospace’s wheel and carbon brake system is designed with thermal management to extend the life-cycle cost over 25,000 miles,” Babin begins. “The wheel and brake system is also designed for 1,400 landings, which is an upgrade for reduced maintenance intervals. Carbon brakes are more durable and resilient than others on the market, and can withstand more landings before seeing signs of wear.
“Landing gear design is typically dictated by fatigue and landing loads; other considerations are environmental and accidental damage that factor into the maintenance programmes that are established during the development cycle of an aircraft, typical for commercial applications,” he continues. “Landing gear transmit ground loads from the wheels and brakes, through the airframe and it is for this reason commercial landing gear is usually type certified by the aircraft manufacturer. There are specific materials used in the manufacturing of landing gear structures to accommodate fatigue, driven mainly by ground manoeuvring such as braking, turning, towing and pushback from the gate. The key monitored parameters include landing cycles, normal and maintenance retraction/extension cycles, shock absorber fluid quantity, nitrogen pressure and dimensional extension in the static state.
“Regional aircraft typically operate shorter and higher frequency flight profiles and are designed to 60,000 to 80,000 landing cycles. Long range commercial aircraft which operate 12-14 hour non-stop flights may be designed to 20,000-40,000 landing cycles,” Babin elaborates. “Generally, maintenance programmes dictate restoration/overhaul intervals defined by flight cycle and calendar intervals, such as 25,000 landing cycles or 12 years, whichever comes first.”
Babin notes, too, that the tracking of structural parts is vital to ensuring compliance to the restoration/overhaul interval and the remaining life of these items, known as life limited parts (LLP). “When a landing gear part reaches its limit, it is then discarded and replaced with new or ‘houred’ item, which has remaining life,” he explains.
Factoring in extremes
While landing gear may be kept in prime condition by those tasked with its upkeep, events such as a hard landing do occur. The whole gear assembly is monitored constantly, so the task when such events occur is to get the observed data to the operator (or its MRO partner) as rapidly as possible for an assessment to decide what repairs, if any, are required.
“Abnormal landing conditions such as being overweight, high descent rate, high energy, runway excursion and towing related are dependent on several factors. These include aircraft weight, roll, pitch and yaw acceleration rates, braking effectiveness and even include the weight of a tow tug for towing incidents,” Babin reports.
“Most of the data would come from the aircraft Flight Data Recorder (FDR) or Quick Access Recorder (QAR), which monitors over 100 aircraft parameters with varying frequency by parameter,” he adds. “Once this data has been downloaded, usually by the airline operator maintenance personnel, it is transmitted to the aircraft manufacturer (type certificate holder) to reduce the data to readable level. This data is then analysed by the aircraft manufacturer and/or the landing gear manufacturer to understand how high the abnormal loading is relative to the design limit load.”
The intelligence gleaned from this data analysis helps pilots to optimise the first and final phases of a flight when the gear is in operation. Learning from the analysis results, takeoff and landing profiles can be adjusted to ensure that as little stress as possible is placed on the gear structure, wheels and brakes. This can even be done for specific airports and also added to routines during pilot training.
On board, according to Babin, the only data that can be provided to pilots is “the status of the landing gear is as it retracts and goes into uplock during the post takeoff phase of the flight and in reverse during the extension and subsequent downlock during final approach on the final phase of the flight.
“Many aircraft are equipped with brake temperature monitoring systems (BTMS) to let pilots know the thermal condition of the brakes following takeoff and, more importantly, after landing. Other pilot indications in the cockpit include the status of steering systems and wheel speed transducers that control anti-skid systems for aircraft brakes,” Babin remarks.
Safety is, was, and always will be the number one imperative in aviation. Monitoring this crucial system, analysing its performance, and using the intelligence gained to deliver that goal is another way in which the industry continues to prove that, as the well-known saying goes, Safety is no accident!
Author: Bernie Baldwin
Published 11 May 2023
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