Part #:

Model: KRA-405B




Radio Altimeter R/T

Part Number :
Davtron Logo




  • 2000 ft. display
  • 28VDC, TSO'd
  • Internal 2500 ft. capability for use with ground proximity systems
  • Used with KNI-415 or KNI-416 indicators
  • Used with two KA-54 or KA-54A antennas
  • Provides analog and ARINC 429 outputs for increased interface capability including GPWS, TCAS, autopilot.
  • Option available with ARINC 552 auxiliary output (-0202 version)
  • Option available that can accept DH input from EFIS or KNI-415 or KNI-416 indicator to generate audio signal (-0202 version)
  • Version available that provides enhanced accuracy (+-2 feet) below 100 ft. using digital 429 buss labels 164/465 (-2001 version)
  • Version available with capacitor (C3) on the RF board changed to dampen frequency response of the high altitude intermediate (IF) receiver filter to low frequencies; RF absorber attenuates stray RF to prevent false low altitudes caused by vibration; 2 thermal conductors change harmonic resonance of the logic and power supply board (-4001 version)
  • Version available to have lower receiver sensitivity than -4001; adds extra margin against possibility of a false low altitude indication when flying above the normal lock range of the rad alt; intended for Dassault FX7 installations with multi-path, low-level reflections or interference that compromises antenna isolation (-5001 version)



Size: 3.00"W x 3.50"H x 11."L Weight: 3.06 lbs. (unit); 5.36 lbs (system)
TSO Compliance: C87/ETSO-2C87 Primary Power: 27.5 VDC ±20% at 850 mA (nom); 18 VDC @ 1.2 Amps (max)
Temperature: -55 to +70C Altitude: 55000 ft.
Accuracy: 3 ft. or +-3% at 0-500 ft. and +-5% at 500-2500 ft. Output: 160 mW nominal, FMCW
Frequency: 4300 +- 15 Mhz Modulation Frequency: 100 Hz nominal
Part Number: Description:
066-01153-0101 Standard unit
066-01153-0202 Includes two options as indicated above
066-01153-2001 Includes option as indicated above
066-01153-4001 Includes option as indicated above
066-01153-5001 Includes option as indicated above


- Radar Altimeter R/T

NSN: 5841-01-552-8117

Price Condition Status
- Radar Altimeter R/T w/ DH output

NSN: 5841-01-561-2819

Price Condition Status
- Radio Altimeter Transceiver
Price Condition Status
- Radio Altimeter R/T w/ Enh. Accuracy
Price Condition Status

Click on a question below to see the answer. If you have a question about this model that is not answered below, please contact

In relation to NE (New) parts, many OEMs change their prices and availability without any notice to dealers or the industry. Therefore, through the REQUEST or RFQ indication, we ask that customers contact us for the most accurate price and availability.

In relation to SV & OH parts, the used parts aftermarket in the aviation industry is not an infinite supply. It is a dynamic, constantly changing market that is significantly affected by and susceptible to highs and lows in supply and demand. Therefore, although we attempt to, at times, we are unable to predict the exact moment when an item may be available. Once again, through the REQUEST or RFQ indication on our website, we ask that customers contact us for the most current and accurate price and availability.

Yes, please see SEA Promotion.

Many avionics systems require a configuration or setup process. This process is required to interface certain avionics systems to other systems in the aircraft that will be inputting or outputting information to and from these systems. Some examples of systems that require a configuration or setup process include:


In addition, most newer technology or solid state systems require configuration via computer interface of some type. A qualified avionics technician should always refer to the appropriate manufacturer's installation manual for complete information and instructions.
Dirty antennas can sometimes cause poor or erratic operation of the radio altimeter system. Especially during winter months, some aircraft's nose wheel's throw dirt and slush onto the antenna. As a preventative measure to keep the antennas clean, a quality aircraft wax can be applied to the antenna.
Display lockup is a commonly encountered problem where the indicator locks up at a low indicated altitude between 5-50 feet. Some pilots will report that the radio altimeter will work normally at low altitudes but after climbing above a certain altitude the indicator locks up. Once the aircraft descends past the locked altitude, the radio altimeter works normally again.

In almost all cases, the cause of lockup is excessive signal leakage between the receive and transmit antennas. Signal leakage is commonly caused by the following situations:

- Antenna reflections hitting an object below the fuselage such as landing gear, skids, or searchlights.
- Poor ground plane between the antennas and the airframe, antennas not mounted on the same piece of metal, or antennas mounted on composite material
Sometimes a pilot may report that the radio altimeter may start indicating altitudes in the rad alt range (0-2500 ft.) at altitudes between 18000-20000 feet. This frequently occurs when flying over a reflective surface such as calm water. What occurs with second time around acquisition is that the receiver detects a return signal that was transmitted two pulses earlier not the transmitted signal it should be receiving. The time between transmitted pulses is equal to a distance in the 18000-20000 ft. range. Therefore, the receiver may process it as though it was signal it was actually trying to receive and then display the incorrect altitude.
Large needle fluctuations is a problem commonly seen when a helicopter is hovering over a soft, diffused surface such as grass. Needle jumps are usually less than 50 feet but can range from hundreds to a thousand feet. Once the helicopter moves forward, the radio altimeter should operate normally again. This needle jumping occurs because the radio altimeter is experiencing decreases in received signal strength. Over a soft, diffused surface, the signal reflection consists of hundreds of small weak reflections with different time and phase, directional qualities. These differences cause cancellations in the total return signal and cause the needle to jump.

To correct this needle jumping, some radio altimeters have an extended dB STC range. This extended range provides an additional receiver gain that can reduce the decreases in signal strength. However, the additional dB gain increase can subsequently increase the potential for display lockup caused by poor isolation between the antennas.
In civilian aviation, these two terms are used interchangeably and essentially mean the same. They both can be abbreviated as "Rad Alt" sometimes as well.

This system measures the between an aircraft and the ground directly below it. "Radar" or Radio Detection and Ranging is the principle by which the system operates. That is, a signal is transmitted towards the ground and then received back for processing. The time the signal takes to reflect back to the aircraft is timed and this is how the altitude is measured. The signal that is transmitted is a radiowave. Thus, this is perhaps this is the reason why some may use the term "Radio Altimeter" instead of "Radar Altimeter".
Yes, the KRA-405B is capable of driving dual indicators. All lines to the indicators can be paralleled including pins A, M, A (underline), and T.
KRA-405B units S/N 3894 and below do not have Mod 9 incorporated during original manufacturing. Mod 9 or Service Bulletin 9 from Honeywell addresses the need to replace the RF board in case of a board failure. Several components on the original RF board are now obsolete. Therefore, a new RF board has been issued for the KRA-405B. List price for the new RF board is $10168. Unfortunately, the KRA-405B logic/power supply board is not compatible with the new RF board and must be replaced also. List price for the new logic/power supply board is $4623. Lastly, the logic/PS board software set must be replaced.

Total Parts cost (List Price) for the incorporation of KRA-405B Service Bulletin is $14791. Thus, this Service Bulletin is not economically feasible to perform.

Negotiating the exchange price of a unit only limits the allowable repair cap for the core unit. Southeast Aerospace's exchange transactions are based on the return of economically repairable core unit. Once the core is received and evaluated, the core repair cost incurred by SEA cannot exceed 75% of the original exchange price. That is, it cannot cost SEA more than 75% of the original OH/SV exchange price collected from the customer. Therefore, when and if an SEA exchange price is discounted, there is a risk that additional charges may be assessed once the core is returned and evaluated.

Some operators prefer to have both visual indication and aural altering of Decision Height from the radar altimeter system. The KRA-405B P/N 066-01153-0202 provides an audio output that can be connected direct to an open selection on an audio panel. Otherwise, for the KRA-405B P/N 066-01153-0101 an external sonalert can be installed for aural altering. P/N 038-00008-0001 is suggested and the KRA-405B installation manual shows detailed information on how to install it.
The "stripline" in all avionics equipment is an assembly that operates in the microwave frequency range (usually.3 GHZ to 30 GHZ) in the RF assembly of the unit. It contains all stages that operate in that range, such as Local Oscillators, RF amplifiers, heterodyne mixers, transmission lines (called waveguides).

Avionics components such as DMEs, transponders, radio altimeters, and weather radars commonly include stripline assemblies.
No, the configuration module is an option that is only needed for installations that require the trip points to be set to a value other than the factory settings, or for installations requiring a zero feet offset.

The installer may alter some of the operational characteristics of the KRA-405B by installing a CM-2000 that has been programmed with custom preferences. These preferences include the threshold altitudes for the 3 Altitude Trip Points and a selectable offset to be applied to all altitude outputs. If these parameters are inconsequential to the installation or the factory presets are acceptable, the CM- 2000 should not be installed with the KRA-405B.