Part #: 622-3201-011

Model: ALT-50A




Collins Aerospace


Radio Altimeter Transceiver

Part Number :




  • Lightweight, low-profile radio altimeter designed specifically for installation in light and medium, fixed-wing aircraft
  • Supplies altitude information to flight control/autopilot system during approach phase of flight
  • Typically used with 339H-3, 339H-4, 339H-4A (helicopter) analog indicators or DRI-55 digital display indicator, and two 437X-1/1A/1B or ANT-50A/51A/52 antennas depending on aircraft configuration
  • Provides decision height selection from 0 to 2000 feet
  • Provides four shop-adjustable altitude trips that can be adjusted to any altitude between 0 to 2000 ft. to provide switching to a flight director or other external system
  • Product improved version of the ALT-50/860F-2 transceiver (i.e. improved altitude accuracy, transmitter output power, etc.)
  • Versions available with altitude error reduction where unit will indicate lower altitude in the event of unit failure thus ensuring safe terrain separation



FAA TSO: C87 RTCA: DO-138, DO-123
ARINC: 408 Environmental Category: DO-138/AG/A/JN/AAAEXXXXX
Temperature: -54 to 71C (operating) Altitude: Up to 45000 feet (operating)
Altitude Accuracy: +-2 ft. or +-2% (0 to 2000 ft.) RF Transmitter Power: 210 mW nominal
Frequency Modulation (Transmit): 100 or 105 Hz Load Capability: 1 millimho maximum
Time constant: 0.09 +-0.01 s DC Analog Signal: 0 to +18 V dc, piecewise linear
Part Number: Description:
622-3201-001 0-2000 ft. range with 4 shop-adjustable altitude trips, 
622-3201-002 0-2000 ft. range, non-adjustable
622-3201-011  Same as -001 but with reduced altitude error product improvement mentioned above
622-3201-012  Same as -002 but with reduced altitude error product improvement mentioned above 


- Radio Altimeter Transceiver

NSN: 5826-01-284-3601

Price Condition Status
- Radio Altimeter R/T (non adj trips)

NSN: 5841-01-074-7161

Price Condition Status
- Radio Altimeter Transceiver
Price Condition Status
- Radio Altimeter R/T (non adj trips)
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.

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".

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.

Yes, the Rockwell Collins ALT-1000 is a fit and form replacement for the ALT-50A. The ALT-1000 includes extensive use of digital technology, end-to-end monitoring and critical level software verification. The ALT-1000 is a single unit designed in a 3/8 ATR short-low package.

ALT-1000 part number 822-1939-025 directly replaces both the ALT-50A part number 622-3201-001 and 622-3201-011.

No, it is not certified to 2500 foot operation, as required by TAWS TSO-C151a.