Heathkit Aircraft Navigation Computer OCW-1401

Date of introduction:  1978 Display technology:  LED-modules
New price:  $169.95 / $274.95 Display size:  14
Size:  6.3" x 3.1" x 1.7"
 161 x 80 x 44 mm3
Weight:  10.6 ounces, 302 grams Serial No:  37313
Batteries:  4*AA Date of manufacture:  year 1979
AC-Adapter:   Origin of manufacture:  USA
Precision:   Integrated circuits:  3 * Mostek MK3870
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 4.6M Bytes)

You are right - there is no connection to Texas Instruments! But - to be honest - it is one of the best engineered calculators. 

If we trace back the Aircraft Navigation Computers back to their roots we locate two different approaches: 
Simple models introduced around 1980 like the
Jeppesen Sanderson avstar or the prostar based on scientific calculators and more complex products like the USMC HARRIER based on programmable calculators.

This OCW-1401 started already in the year 1978 a third approach: Powerful Navigation and nothing else! Later products like the Navtronic Explorer (1983) and the Jeppesen Sanderson Techstar (introduced 1992) continued these kind of products.

OCW-1401_2.jpg (116786 Byte)You are familiar with this OCW-1401? Then you know the calculators sold by National Semiconductors. On a first view the calculator looks like a scientific calculator from National Semiconductor, e.g. the Model 4650. Indeed, the keyboard and the display of them are identical.

The OC-1401 was sold as kit, the OW-1401 was factory wired. Both included:

The calculator
A glare screen for the display.
A cigarette lighter plug for external power.
A hard case to protect the equipment.

OCW-1401_PCB.jpg (44316 Byte)Dismantling this Heathkit OC-1401 Aircraft Navigation Computer reveals the complexity of the product. Three mask-programmed 8-bit single-chip microcomputers manufactured by MOSTEK (MK3870-MK14103 to 14105) and three other IC's (Fairchild F3539, National Semiconductors DS8664 and DS8667 display drivers) on a huge printed circuit board. To our knowledge the most complex pocket calculator ever produced - like most Heathkit products it was sold as a kit! A factory assembled version was available at $274.95. Find more information about the MK3870 here

OCW-1401_1.jpg (41149 Byte)More astonishing is the usage of the calculator. In comparison to other flight computers you don't need a 100+ pages manual. Three modes are available:

Preflight: You have to key in all preflight data with the orange keys.
   Data is saved in standby mode while transport to airport.
In-flight: You set the time and key in all necessary data with the yellow keys.
Navigation: With the green keys you get all navigation data.

If we trace back in the history of electronic flight computers we discover: The Commodore N-60, this Heathkit OCW-1401, the navtronic 16 and the Texas Instruments TI-58 (with installed Aviation Modul). Heathkit published a small comparison table:

Features Heathkit OCW-1401 Commodore N 60 Navtronics 16 Texas Instr. TI-58
Flight Leg Entries Up to 9 1 1 1
Continuous Data Update YES NO NO NO
Built-in Clock/Timer YES NO NO NO
Fuel Warning YES NO NO NO
Built-in Diagnostic YES NO NO NO
Scientific Functions YES YES NO YES
Internal Program Built-in YES YES YES NO
Price $169.95 (KIT) $99.00 $197.50 $149.95

All were introduced in or before 1978, two years till the Jeppesen Sanderson avstar based on a Texas Instruments TI-35 appeared.

Don't miss the Tamaya NC-77 Astro-Navigation Calculator!


The 8-bit single-chip microcomputer MK3870 was introduced already in 1977.

In the beginning of microprocessor production Mostek was a second source of Fairchild's F8. Both designed one-chip microcomputers around the F8. Fairchild designed the F3859, which was a simple combination of the F3850 CPU and F3851 PSU on a single chip. Mostek developed a more ambitious one-chip microcomputer, the MK3870. Mostek developed this MK3870 ahead of the Fairchild F3859. Therefore, Fairchild dropped the F3859 and became a second source for the 3870.


The MK3870 is a complete 8-bit microcomputer on a single MOS integrated circuit. It is manufactured in a N-Channel ion injection silicon-gate technology compared to the ion-implantation, depletion-mode load, P-channel MOS process of the MK5020. The MK3870 can execute the F8 instruction set of more than 70 commands, allowing expansion into multi-chip configurations with software compatibility. The device features 2048 bytes of ROM, 64 bytes of scratchpad RAM, a programmable binary timer and interrupt, 32 bits of TTL compatible I/O and a single +5 V power supply requirement.


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If you have additions to the above article please email:

Joerg Woerner, December 5, 2001. No reprints without written permission.