| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
At about 2000 local time on 21 June 2021, the crew of a Gates Learjet Corporation Model 36 aircraft taxied to depart from Nowra, New South Wales. During the taxi, the crew had difficulty turning the aircraft.
After take-off, the crew received an unsafe landing gear indication when the wheels were retracted and in response, elected to extend the landing gear. When the landing gear was extended, the crew observed a normal cockpit indication and returned the aircraft to Nowra. A fly-by inspection revealed that the nose landing gear, while extended, was oriented side on to the direction of travel. Upon touchdown the nose wheel quickly straightened, and the landing roll proceeded without further incident.
After the flight, maintenance engineers inspected the aircraft. Their assessment was that during landing gear retraction, the uplock roller failed to engage the uplock latch because the roller was facing downwards after rotating through 180º during taxi. Prior to landing, the nose wheel was reportedly oriented side-on to the direction of travel. This is likely to have occurred when the crew extended the landing gear and the centring mechanism attempted to correct the orientation of the nose wheel.
Figure 1 shows the normal operation of the nose wheel landing gear when it is retracted. The uplock roller attached to the lower portion of the nose wheel landing gear leg is captured by the uplock latch in the wheel well. This closes a switch which provides the crew with a landing gear up and locked indication in the cockpit.
Prior to the flight, the aircraft’s nose wheel landing gear steering was marked on the maintenance release[1] with a Minimum Equipment List[2] (MEL) entry to notify the crew of a known fault with the system. The crew had signed the maintenance release and were aware of the defect. This fault affected the pilots’ ability to manipulate the nose wheel, however, steering was still possible through the use of differential braking. The flight manual specified that while operating with degraded steering performance, tight turns were to be avoided. The difficulty the crew experienced while positioning for take-off is likely due to the castoring lower portion of the nose wheel landing gear arm rotating through 180º to face in the opposite direction.
Figure 1: Normal operation of the nose wheel landing gear uplock
Source: ATSB
Safety action
As a result of this occurrence, the operator has advised the ATSB that they have taken the following safety actions:
- The crew were alerted to the potential risks of the nose wheel being reversed due to sharp turns and the likelihood of experiencing turning difficulties.
- Procedures were introduced to manage a possible reversed nose wheel during taxi.
- Updated guidance was provided regarding the positioning of aircraft for dispatch when nose wheel steering was unserviceable.
- Engineering held a meeting to highlight the importance of correct strut servicing and the identification of potential traps or error points.
Safety message
This incident highlights the importance of adhering to manufacturers’ recommended operating procedures, especially those imposed by Minimum Equipment List conditions. The Civil Aviation Safety Authority publication CAAP 37-1 Minimum Equipment Lists explains the intention of the MEL process.
Its purpose is not to encourage the operation of aircraft with inoperative equipment. Such operations are permitted only as a result of careful analysis of each item to ensure the required level of safety is maintained.
A thorough understanding of aircraft systems is required for a crew to accurately assess the effect a particular defect has on normal operations.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report and allow for greater industry awareness of potential safety issues and possible safety actions.
_________
- Maintenance release: an official document, issued by an authorised person as described in Regulations, which is required to be carried on an aircraft as an ongoing record of its time in service (TIS) and airworthiness status. Subject to conditions, a maintenance release is valid for a set period, nominally 100 hours TIS or 12 months from issue.
- Minimum equipment list: A document created specifically to regulate the continued operation of an aircraft with inoperative equipment under certain conditions or limitations. /a>