Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
AIR-21-14
August 24, 2021
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) alerts owners
and operators of Robinson Helicopter Company R44-series and R66
helicopters equipped with the optional HeliSAS autopilot system that
the system may fail to automatically disengage in the presence of a VHF
NAV or glideslope flag indication on the PFD. The affected Robinson
helicopters are limited to the R44-series and R66 equipped with both
the HeliSAS autopilot and a Garmin PFD.
At this time, the airworthiness concern is not an unsafe condition that
would warrant airworthiness directive (AD) action under Title 14 of the
Code of Federal Regulations (14 CFR) part 39.
Background
While conducting a practice ILS approach during a production flight
test of a Robinson R66, the pilot noted a short duration glideslope
flag indication on the PFD. The autopilot remained engaged but was not
receiving vertical guidance to continue down the glidepath, so the
helicopter remained in level flight. When the flag cleared a few
seconds later, the helicopter was above the glidepath and the autopilot
pitched down to recover.
The HeliSAS autopilot system is designed to disengage vertical guidance
in the presence of a glideslope flag and lateral guidance in the
presence of a NAV flag. The flag signals are sent from the Garmin PFD
to the autopilot Flight Control Computer (FCC) via an interconnecting
wire harness. The electrical signal sent by the PFD is such that a
resistive load must be on the line for it to be properly interpreted.
Some helicopters were manufactured without the appropriate resistors
installed. Autopilot operations using GPS navigation are not affected
because GPS status is communicated to the autopilot using different
wires and signal types.
In August 2020 Robinson issued Service Bulletin SB-106 for the R44
series and Service Bulletin SB-37 for the R66, both dated August 21,
2020 with instructions to retrofit resistors to aircraft in the field.
Recommendations
We recommend that owners/operators of Robinson R44-series and R66
helicopters comply with R44 Service Bulletin SB-106 and R66 Service
Bulletin SB-37, both dated August 21, 2020.
For Further Information Contact
Thanh Tran, Aerospace Engineer, 3960 Paramount Blvd , Lakewood, CA
90712, United States; phone: (562) 627-5304; fax: (562) 627-5210;
e-mail: thanh.b.tran@faa.gov.
For Related Service Information Contact
Robinson Helicopter Company, 2901 Airport Drive, Torrance, CA 90505;
telephone 310-539-0508; fax 310-539-5198; or at
https://www.robinsonheli.com.