Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
SW-10-41
August 5, 2010
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin advises you of an
airworthiness concern regarding potential unannunciated failures of the
MK XXII Enhanced Ground Proximity Warning System (EPGWS) aural alerting
function. 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 Aviation Regulations (14 CFR) part 39.
Background
Honeywell issued a Service Information Letter (Publication Number
D201004000029), dated April 16, 2010, stating that the MK XXII EGPWS
used in helicopters will experience an unannunciated loss of the
Terrain Awareness Warning System (TAWS) aural alerting function if the
radio altimeter is in either the no computed data (NCD) state or the
radio altimeter data invalid state at takeoff. The EGPWS terrain
display will still be active and accurate except for the lack of alert
(caution or warning) indications. Once the radio altimeter transmits
valid data, the TAWS aural alerts will become fully functional for the
duration of the flight, even if the radio altimeter subsequently
encounters a NCD condition. Honeywell is working on a software
modification to correct this problem. The software update is expected
to be available in the fourth quarter of 2010.
In the interim, owners and operators of helicopters equipped with
Honeywell MK XXII EGPWS systems need to be aware that the TAWS aural
alerting function may become non-functional due to a radio altimeter
data invalid or NCD state. This SAIB is to make rotorcraft owners and
operators aware of the problem and of the proposed forthcoming
solution. When Honeywell makes the software upgrade available, we will
revise this SAIB to communicate this information to you.
For Further Information Contact
George Schwab, Aerospace Engineer, FAA Rotorcraft Directorate,
Rotorcraft Standards Staff, Safety Management Group, 2601 Meacham
Blvd., Fort Worth, TX 76137; phone: (817) 222-5114; fax: (817)
222-5961; e-mail: george.schwab@faa.gov. The Service Information Letter
can be viewed at Honeywell’s website at:
http://portal.honeywell.com/wps/portal/aero.