Part #: 4004437-901

Model: RT-220






Radio Altimeter R/T

Part Number :

  • Radar altimeter transceiver utilized in AA-200 Radio Altimeter System
  • High resolution, short pulse radio altitude system
  • Provides an absolute altitude display from 0 to 2500 feet
  • Version -901 provides a trip switch output for altitudes of 50, 250 & 1250 feet
  • Version -902 (RT-221) provides the same trip switch outputs as -901, with the addition of a trip point at 400 feet
  • Version -903 (RT-220H) has an output memory of 3 seconds
  • All versions are out of production



Dimensions: 7.53"D x 10.96"W x 4.16"H Weight: 7.0 lbs max
TSO: C-87, AAAAAX Power Requirements: 21-31 VDC, 1.5 amps max
Temperature: -54°C to +55°C operation -62°C to +71°C storage Altitude: 0 to 45,000 ft
Peak Power Output: 70 watts nominal RF Freq.: 4.3 GHz
Operation Altitude: 0-2500 ft. IF Freq.: 60 MHz
Part Number Description:
4004437-901 RT-220, Trip points: 50, 200, 1250 ft, Radio Altimeter
4004437-902 RT-221, Trip points: 50, 200, 400, 1250 ft, Radio Altimeter
4004437-903 RT-220H, Trips points as -901, Output Memory of 3 seconds, Radio Altimeter


- Radio Altimeter R/T

NSN: 5841-01-003-1964

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.

The Sperry/Honeywell RT-300 can be used as a replacement for the RT-220 as long as Pin E in the RT-220 mating connector is jumpered to Pin N. Of course, the mounting trays would need to be changed to compensate for the size differences between the two units.
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.

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.