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AN/ALQ-172 Countermeasures System (CMS)

The AN/ALQ-172 Countermeasures System (CMS) radar warning system provides the B-52H, AC-130U, MC-130H and other aircraft with electronic countermeasures against airborne and ground based fire control radar systems and associated missiles. It decreases the effectiveness of weapons associated with threat radar emitters, thereby providing a Self-Protection feature. This Digital Frequency Discriminator [DFD] based system determines pulsewidth, AOA (angle of arrival) and PRI of a detected microwave signal to aid in deinterleaving and signal processing, resulting in a complete low power receiver. Delay line ratios provide the best possible phase margins to minimize ambiguity errors, and frequency and amplitude words are temperature corrected for improved accuracy.

Design engineers originally developed the AN/ALQ-172(V) ECM system in the early 1980s as an upgrade to the B-52G/H ECM suite. The system provided various ECM techniques against airborne and ground-based fire control systems and associated missiles. In 1996, analysts from the Battelle Memorial Institute, Columbus, Ohio, conducted a study which showed that malfunctions in and repair of the AN/ALQ-172 system caused the highest cost per flying hour (CPFH) of any system on the B-52 aircraft. Based on this study the Air Force, through Engineering Change Proposal (ECP) 93, instituted an AN/ALQ-172 modification program designed to improve the memory and processing capability of these systems. At the end of FY97, they had also reported that an additional AN/ALQ-172 system was needed to provide full threat protection.

The Enhanced ALQ-172 is an upgrade to the existing ALQ-172(V)1 on the AC-130U and MC-130H aircraft. This upgrade consists of upgrading LRUs 1, 3, 4, & 10 and replacing LRU 2 with LRUs of the ALQ-172(V)3 configuration. This upgrade consists of the replacement of the existing ALQ-172 High Band Line Replaceable Units (LRUs) with the ALQ-172(V)3 configured High Band LRUs. All ALQ-172 LRUs which are part of the Enhanced ALQ-172 shall not be integrated to the existing avionics busses to any greater extent than the current ALQ-172(V)1. The associated Low Band Jammer (LBJ) RF Countermeasures on the AC-130U and MC-130H aircraft is a SOF-common system, either the ALQ-172(V)3 or the ALQ-196. As a goal, the LBJ integration shouldl not cause the MC-130H's aircraft Mission Computer Operational Flight Programs to be rewritten. Any proposed MC-130H mission computer OFP changes shall be subject to approval by the contracting officer. The system shall have the capability to be integrated with other defensive avionics using a data bus in the future. As a minimum, the integrated aircraft system shall maintain current aircraft display capabilities.

In FY96, the Air Staff issued PMD 2318(2)/PE1160404BB directing Warner Robins Air Logistics Center personnel to install AN/ALQ-172(V)3 ECM Jammers on AC-130H Gunships. The most recent version of the AN/ALQ-172(V) system incorporated Engineering Change Proposal ECP-93, mentioned in the earlier B-52 section. This ECP embodied R&M improvements and a low-band frequency extension to augment the existing AN/ALQ-172(V)1 system which had been installed previously on other Special Operations Forces' (SOFs') C-130 aircraft. Plans called for the new system to replace the non-supportable AN/ALQ-131 ECM pods as the primary RF jammer for AC-130H aircraft. Early in the 1990s, the AN/ALQ-172(V)1 system, which had only the high- band ECM capability, had been installed on SOF AC-130U, MC-130H, and MC-130E aircraft. It consisted of two identical sub-systems, one aft and one forward, controlled by a common display and control unit. Engineers modified the AN/ALQ-172(V)3 system, which had a similar configuration, by adding low-band transmitters, antennas, and antenna control units.

Center officials subsequently let two contracts; the first was the AN/ALQ-172(V)3 Group B Contract and, the second, a Group A Contract. During FY96, LN leadership contracted with International Telegraph and Telephone (IT&T) Avionics (ITTAV), Atlanta, Georgia, for development of the AN/ALQ-172(V)3 Group B equipment. Engineers developed all of the Group B equipment, except for the low-band extension, under the previously mentioned ECP-93. Under tenets of the contract, ITTAV employees became responsible for the creation the low-band equipment and integrating the low-band extension into the basic AN/ALQ-172 system.

Even as ITT personnel worked on the Group B contract, Center management completed the ALQ-172 Group A Contract. As such, Group B workers provided Group B equipment to the Group A contractor which was Raytheon E-Systems, Waco Division (RES-W) Waco, Texas, previously Chrysler Technologies Aerospace Systems (CTAS). Plans called for RES-W personnel to integrate the Government Furnished Equipment (GFE) onto the AC-130H Gunship. Integration tasks included structural mounting, aircraft wiring, system cooling, system pressurization, and blanking. In fact, officials of the Center's SOF SPO/Directorate (WR-ALC/LU) competitively awarded RES-W a Final Full Production (FFP) contract for design and implementation of the Group A installation. To this end, the two parties finalized a Statement of Work (SOW) which specified requirements which made reference to the user supplied Requirements Correlation Matrix (RCM) and the Group B Prime Item Functional Specification (PIFS). Subsequently, they also concluded an Associate Contractor Agreement (ACA) between RES-W and the Group B contractor ITTAV which stipulated that both contractors would work together on the overall modification and installation program.

During FY97, ITTAV workers nearly completed Design Verification Tests (DVT) for the AN/ALQ-172(V)3. One Problem Trouble Report (PTR) remained outstanding but was being worked. The work force corrected and updated all other specified PTRs which Center technicians infused into the Group B equipment which, in turn, were provided to RES-W employees for installation on the AC-130H aircraft. During FY97, they had already completed trial installation of the AN/ALQ-172(V)3 system on AC-130H Gunship Serial Number (S/N) 69-6574 and all non-Electronic Combat (EC) ground tests. Even so, by the end of the fiscal year, four problem areas on the overall AN/ALQ-172(V)3 installation continued to be worked.

The first of these issues was the isolation between the aft AN/ALQ-172(V)3 Low- Band Phased Array Xmit Antennas, LRU-14 located in the "beaver-tail" area, and the Low-Band Omni-Receive Antenna, located at the tip of the vertical stabilizer. Personnel discovered that the antennas were approximately 10 decibels (dB) below what ITTAV analysts determined was required. As a result, a ring-around effect occurred during ground testing. Thus, LUG employees attempted to conduct a flight test to determine if the problem repeated itself while in flight. Unfortunately, basic aircraft failures and lack of aircrew availability delayed the required sortie throughout much of FY97.

Immediately following their identification of the aft isolation problem, LUG personnel, in conjunction with ITTAV and RES-W technicians, attempted to solve the isolation issue through analysis and experimentation on the aircraft itself. Even as the fiscal year ended, no solution had been identified. Nonetheless, experiments did result in a nearly 3dB improvement. Unfortunately, the ring-around remained, at least on the ground. At the same time, the anomaly never appeared in flight.

A second issue focused on LRU-14 Cooling. As part of the SOW, RES-W provided LRU cooling requirements in the system PIFS under Revision A of the PIFS. Subsequently, Revisions B and C of the AN/ALQ-172(V)3 PIFS significantly increased cooling air flow requirements for the Low-Band Phased Array Antenna System (LRU-14). By the end of FY97, due to the timing of the later revisions, the Group A design and trial installation reflected Revision A requirements and did not provide sufficient cooling (as defined by the system developer) to the Group B LRU-14s which were of short supply.

At the same time, Center officials requested that RES-W upgrade the LRU-14 cooling system to meet revised requirements. Due to long-lead times and the time required to make a contract change and review the proposal, the eventual long-term solution, the revisions could not be completed during FY97. Well aware of this situation, LUG leaders decided to allow the test program to proceed while they sought a short-term solution which, even if it did not fully meet air flow requirements, did provide sufficient cooling to pass the Quality Test and Evaluations (QT&E) and Operational Unit Evaluation (OUE). This short-term fix replaced the four contractor-installed cooling fans with off-the-shelf higher capacity fans that were nearly form-fit replacements. Personnel also replaced aducting gaskets with thicker gaskets to fill air flow leaks and increase cooling air flow.

A third problem involved the Blanking Interface Unit (BIU) provided by the Group A contractor. It failed to pass all blanking ground tests due to serious deficiencies. The contractor notified the BIU subcontractor who implemented fixes and, on 18 July 1997, installed a new unit, thus correcting all deficiencies, and allowing the new unit to pass ground tests.

The final issue dealt with the Forward Xmit Radome Attachment. In the summer of 1997, during the trial installation process, LUG management observed that the forward AN/ALQ-172 radome attachment scheme lacked a sufficient number of fasteners to prevent water intrusion on a long-term basis. Contractor officials took issue with LUG's engineering evaluation arguing that the attachment scheme was adequate and met contract requirements. Over the remainder of FY97, additional forward radome attachment issues were revealed. By the end of the fiscal year, removal and replacement times had delayed the SOW timetable. Concurrently, RES-W management agreed to redesign the forward radome attachment installation and, after design approval from LUG, implement the change on the kit-proof aircraft. Plans called for the trial installation aircraft to be retrofitted with the new design during the modification effort.

By the end of FY97, the installation program was well underway. Most of the problems faced had been solved, and those still being worked were well on their way to solution. In the case of the isolation issue, the work force continued to work the matter on the ground while they awaited a flight-test sortie that they finally got. This provided only partial answers, thus, officials had to determine if they should continue to attempt to solve this problem prior to entering EC ground and flight testing or enter final testing with a known problem and attempt to fix it later.

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Maintained by Robert Sherman
Originally created by John Pike
Updated Saturday, April 22, 2000 9:42:39 AM