Compliance with Manufacturers Service Bulletins is essential under which condition?

Compliance with Manufacturers Service Bulletins is essential when these bulletins are accompanied by an Airworthiness Directive (AD). An AD is a legally enforceable regulation issued by the FAA to address safety issues related to aircraft, engines, propellers, or appliances. When a service bulletin is tied to an AD, it signifies that the FAA has determined that the information or modifications outlined in that bulletin are critical for maintaining the airworthiness of an aircraft.

Therefore, aircraft operators are required to comply with the AD to ensure that their aircraft remain safe and comply with federal regulations. This emphasis on safety and regulatory compliance is paramount in aviation, making adherence to any associated service bulletin a crucial responsibility of the technician and the aircraft owner.

In contrast, the other conditions listed may suggest the importance of service bulletins, but they do not carry the same legal enforcement or critical safety implication as an AD. For example, the necessity deemed by an aircraft owner or operational efficiency may prompt attention to a service bulletin, but these do not mandate compliance in the same way that an AD does.