EASA SIB SW-10-41: Honeywell MK XXII Enhanced Ground Proximity Warning System (EGPWS) Software Problem

What to do

Helicopter owners and operators equipped with the Honeywell MK XXII EGPWS should be aware of the potential loss of TAWS aural alerts if the radio altimeter is invalid or in NCD state at takeoff. They should monitor Honeywell's release of the software update expected in late 2010 and plan to install it once available. No mandatory compliance deadline is set, but operators should maintain heightened awareness until the software fix is implemented.

Summary

The Special Airworthiness Information Bulletin SAIB: SW-10-41 addresses a software problem in the Honeywell MK XXII Enhanced Ground Proximity Warning System (EGPWS) installed in helicopters. This issue involves a potential unannunciated failure of the Terrain Awareness Warning System (TAWS) aural alerting function when the radio altimeter is in a no computed data (NCD) or invalid state at takeoff. The bulletin informs operators that while the terrain display remains accurate, the aural alerts may not function properly until valid radio altimeter data is received.

What changed

This bulletin introduces awareness of a software issue affecting the Honeywell MK XXII EGPWS where the TAWS aural alerts may not activate if the radio altimeter is invalid or in NCD state at takeoff. Honeywell is developing a software update expected in the fourth quarter of 2010 to resolve this problem. Until then, the bulletin serves as an advisory to helicopter operators about the potential alerting deficiency.

Why it matters

This information is critical for aviation professionals, especially helicopter operators and maintenance personnel, because the lack of aural TAWS alerts could reduce situational awareness during critical phases of flight. Understanding this issue helps ensure that operators remain vigilant and do not solely rely on aural warnings for terrain avoidance. It also informs maintenance and compliance teams about an upcoming software update that will restore full functionality.