Honeywell KLN94 SDDR-31 USB CompactFlash Writer

This material is here in case Honeywell remove it from their website. This handy product has been unsupported for some years. Bizzarely, Honeywell delegated the sales of this product to a private individual living in the USA; as of mid 2009 he still had some stock. If this capability is lost, it will leave the laptop-KLN94 direct-connection method as the only way to update the KLN94 database.

There used to be a PCMCIA-attached writer also but I never saw one for real and according to Honeywell it worked only under Win98.

Fortunately the retail SDDR-31 product can still be found on Ebay - search for "sandisk imagemate" or similar and make sure it is an SDDR-31 and not e.g. an SDDR-55 which looks identical.

The following stuff is from the Honeywell website here (local copy)

SDDR-31 Operating Instructions (300k)

GPS Database Help Info Download Instructions

v1.5 GPS Database Loader (Win98-WinXP 1.7MB)

The above database loader (v1.5) works OK but the following later release (v1.7) is claimed to work on Win95 through to Vista:

v1.7 GPS Database Loader (1.7MB)

and there is an "alternative" version of it

v1.7 alternative Database Loader (1.7MB) Readme.txt

In 2015, some new files were found on the Bendix King site:

Win7-GPS Data Loader readme . doc file (this program was tested 17/10/2017 under Windows 7 64 bit and worked fine)

Windows Standard-GPS Data Loader (probably identical to the above v1.5)

Windows Vista-GPS Data Loader Option 1

Windows Vista-GPS Data Loader Option 2

These descriptions were also provided

I can confirm that contrary to what the above suggests, the Imagemate does work under winXP SP3! But not on just any computer. I have two of them running on two fairly normal computers, ~3GHz desktops.

There is also an old DOS database loader netload.exe whose function seems to be limited to programming the KLN94 via the download cable, i.e. it does not drive the SDDR31 CF writer. I have never tried this program but running it shows the available options; these do not include extracting the database key from the CF card so I cannot see how it fits in with the current Honeywell database downloading scheme which requires the database key to be entered into the website before the download can commence...

The following firmware update needs to be applied to the retail SDDR31 product, to enable it to access the specially hacked KLN94 cartridges. A Win98 computer with a USB port is required to perform this update; other operating systems will not work.

Sandisk SDDR-31 Firmware Update (1MB)


KLN94 Firmware

The above v1.5 GPS database loader offers an option to update the KLN94 firmware also but I have never seen the binary data file which it asks for. Normally this update is done by dealers.



The KLN94 CF cartridges are actually Sandisk 48MB ones; not the 192MB shown in the above pic. However, retail CF cartridges cannot be used (even if you could find a 48MB one - years after they have been discontinued) due to the Honeywell copy protection scheme. I have no idea what kind of hack Honeywell did, but it certainly is a nonstandard filing system (not FAT16/FAT32). Moreover, reading physical sectors from the cartridge (in any CF reader) returns mostly nulls and a bit of garbage, so they might have used some undocumented feature of the FLASH chips used by Sandisk during that era. I only hope they have bought a big enough stock....

When you go to the Honeywell website to download the database, you have to specify the database key. This consists of eight hex digits e.g. 45AAB78F. This key is stored on the CF card. It is not stored in the KLN94. The above GPS Database Loader includes a function to retrieve this key from the CF card - either via the SDDR31 writer, or via the KLN94 download cable. This retrieval is an essential step before downloading the new database. The key does not normally change, and many pilots write the key on the CF card, but beware: the database loader does sometimes change the key to a new random number!!! Why it does this is a mystery; one reason might be to limit how many databases can be downloaded under the same database key, to make database cryptoanalysis harder.

The database loader is not 100% reliable and sometimes it does not recognise the card in the SDDR31. It asks whether one has inserted a different (non-KLN94) card into the reader; one has to reply one way or the other and I can never remember which reply then makes it work...

There are two ways to update the KLN94 database: by programming the CF card in the SDDR31, or by programming the KLN94 memory directly via the download cable. I don't think the latter option does anything with the CF card plugged in the KLN94 (whose database could then be very old) and this also means the database key would never change.

The KLN94 is a dead product now. As of about 2003, Honeywell washed their hands of all development of it. They have confirmed in writing it will never be authorised for PRNAV, although it is fine for all other IFR operations including approaches. More information on the KLN94 and replacement options can be found here in the avionics upgrades section. Manufacture stopped in 2011.

The KLN94 has no digital (ARINC) autopilot outputs but has an unusual GPSS/roll steering output which is analog and which works only with the KFC225 autopilot. From pilots' feedback, this analog connection works adequately for normal flight including flying the T-shaped GPS approaches.


Update 10/2019: this appeared on the Honeywell website.


This page last updated 3rd October 2019

Contact details