• Measures radar height above terrain up to 2,500 feet
• Accurate to within two feet at the critical low altitudes
• Provisions for single installations on Category II certifications (ALT-4000)
• Provisions for dual or triple installations in Category IIIa certifications (ALT-4000)
• Versions with analog outputs capable of driving existing indicators
• Analog outputs in ALT-55B or ARINC 552A format - strap selectable (ALT-4000)
• Available with standard or shop-adjustable trips
• Four ARINC 429 digital buses eliminates external converters (ALT-4000)
• Full temperature/altitude capability
• Stringent lightning and HIRF hardening
• Lightweight at 4.7 pounds, plus additional aircraft installation delay selections that can reduce antenna cable weight
• Front panel computer port for system configuration and access to system faults
• Computer interface that allows for flight simulation to aid checks of associated systems
• Versions compatible with Collins FPA-80
• Versions that directly plug in and replace the ALT-55B or ALT-50A

The ALT-1000/4000 Radio Altimeter extends the long tradition of dependable performance and high integrity of Collins low-range radio altimeters. The ALT-1000/4000 architecture is distinguished by exclusive use of digital techniques, full end-to-end monitoring and critical-level software verification.

The ALT-4000 is intended for single installations certified for Category II and for dual or triple installation in Category IIIa automatic landing systems.

The ALT-1000/4000 is a single unit packaged in a 3/8 ATR short-low package. The package and aircraft mounting are identical to the ALT-55B.

FMCW is the simplest of radar ranging techniques and the most resistant to false lock to undesired targets such as aircraft structure or landing gear. With proper antenna installation, the FMCW processor accurately selects the terrain directly below the aircraft for ranging and ignores seasonal effects of snow or leaves on vegetation.

FMCW ranging measures range by mixing a sample of the constant power, linearly varying frequency transmitted signal with the signal reflected from the target. The difference produced is a constant low frequency proportional to the range to be measured. The broad beam of the antenna system illuminates a large area of the underlying terrain. It allows for correct operation over the normal range of aircraft pitch and roll with a fixed antenna system, and a simple limiter selects the correct ray.

The ALT-1000/4000 is available with adjustable or standard trips and with optional analog outputs. The ALT-4000 analog versions provide two isolated outputs in either ALT-55B or ARINC 552A format to interface with existing systems. Rear connector pin strapping selects the desired analog format.

The four isolated ARINC 429 altitude outputs are provided on the ALT-4000 for connectivity to Pro Line 4 and TCAS systems.

A separate RAC-870 Radio Altimeter Converter is required if there is a need to convert analog altitude data from the ALT-1000 into an ARINC 429 serial format. No separate adapter is required with the ALT-4000.

The ALT-1000/4000 is 4.7 pounds and provides selections of aircraft installation delays, reducing or eliminating the coils of coaxial cable required to zero the system.

ALT-1000/4000 retains the high accuracy and resolution required of all Collins radio altimeters for decision height indication and, in automatic landing systems, source data for pitch guidance to touchdown.