Boresight Tower Inspection Report R20200613_Redacted.pdf

New Boston Air Station

Boresight Tower Inspection

The inspection crew arrived on site 05 November 2019 with the following team members:

Our scope of work on this visit was to troubleshoot the inoperable tower light system, measure and evaluate the guy cable system, visually inspect tower and test the tower ground system.

The project began with a visual inspection of the tower straightness, guy cable sag and anchor system;

all appear acceptable and the tower was deemed to be safe to climb. The tower light system was completely inoperative with none of the L864 beacons nor any of the two 3-blub elevations of L810 Marker lights.

Our engineer and one climber began the anchor inspection, tension verification, tower straightness and anchor positions. The tower anchors have concrete encased anchor rods with spreader plates to accommodate the multiple guy cables in the guy lanes. This team using wire brushes and cold galvanizing paint spray removed rust and conditioned the assemblies as shown in the following photo.

Typical anchor assembly

Tower Lighting Systems:

1. The remaining two-man team began troubleshooting the lighting system in the light controllers at the base of the tower. There are three controllers, one for each of three L864 beacon assemblies on the tower.

2. The below photo is the interior of the first light controller and is the Master while the mid-level beacon controllers are slave.

3. Visual inspection reveals:

a. Note the oil on the bottom of the cabinet, this oil in semi-solid form is used to insulate the windings and absorb heat during operation. The transformer has been exposed to excessive heat condition causing the component to overheat and melting the grease.

b. The above fault condition is the cause of the top beacon being inoperable.

c. This condition is not correctable, and the transformer must be replaced.

d. The replacement of the transformer is obvious, the cause of the failure is unknown

e. Our recommendation and that of the factory tech support is to return the controller and not attempt component replacement in the field.

4. The remaining two light controllers are used to manage the two mid-level beacons.

a. Controller #2 is a slave unit of the master controller and manages the one beacon closest to the access road. During troubleshooting the control relay contacts were cleaned and manually operated, this action resulted in the red only light to illuminate.

b. The white day light remains unlit due to other problems believed to be caused by a defective trigger circuit board discovered during further troubleshooting.

c. Our recommendation is to Replace or return this unit to the factory for analysis.

d. Marker Lights:

1. Controller #2 also controls the operation of the upper and lower elevations of marker lights that are non-operational, testing revealed no voltage to the marker systems. Further troubleshooting revealed a non-functioning relay controlling this voltage to the marker system. This fault in the relay is believed to be in the relay or the control circuitry designed to operate the relay.

2. The marker lights (6) are incandescent 117w aviation bulbs that need to replace annually and in addition, the current FAA directive has deleted the requirement for these marker lights when used with a three-beacon configuration. Our recommendation is after the repair, remove the marker light system and discard

3. The replacement circuit cards are available with a 2-3-week delivery. However, this might not be all that is defective in the controller but must be replaced before further troubleshooting can proceed.

4. Our recommendation is to return this box to the manufacturer for recondition or replacement.

e. Controller #3 is completed inoperable with visually defective trigger circuit board components, defective interlock switch and no power from the Master Controller. Our recommendation for restoring service is same as Controller #2, return the factory.

5. The existing tower light system was installed in 2003 and has passed its recommended life cycle.

With multiple problems in each of the three controllers our recommendation is a complete replacement of the system. The existing system can be replaced with a like system however, our recommendation is to upgrade to a near maintenance free LED system.

6. LED Tower lighting system:

a. Recommendation - remove and replace existing systems with a modern upgraded LED system. These new LED blubs have an average “Mean Time Between Failure (MTBF)” of 50,000 hours.

b. In addition, the controller circuits operate under very low current, typically less than 5 amps extending the life cycle to nearly the life cycle of the LED Lamp.

Tower Ground System:

1. Photo #1 shows a property installed “Earth Ground Electrode System” using a combination of a ground well and larger diameter (500 mcm) copper cable radial buried along the full length of the access road.

2. Photo#2 shows the test equipment and the ground resistance display of 4.3 ohms. The requirement given by the New Boston Air Station Command is to have a resistance reading of less than 25 ohms.

3. No action is considered or recommended on this system!

Drilled Ground Well System Excellent tower ground resistance

Structural:

The visual inspect of the tower base reveals several unacceptable conditions that will affect the integrity of the tower structure as follows:

Rust egress into tower base steel

Abandoned electrical components

1. These photos show an abandoned enclosure mounted to the tower base frame. The unistrut is severely rusted. This corrosion will migrate to the tower base and eventually, degradation to structural integrity of the tower.

a. Solution is to remove and discard the abandoned material and components

b. Treat and recondition the effected tower steel sections

2. Our team of climbers ascended the tower to top of the structure inspecting each supporting section

3. In addition to the visual inspection for damaged and corrosion at each 20’ section, we performed spot checks of tower leg steel thickness using an ultrasound meter.

4. The measurements were given to our engineer who determined all sections are within acceptable tolerance.

5. In sections 15-20 the paint and the galvanized coating are nonexistent, and surface rust has developed.

6. Our recommendation is to remove this surface rust and apply a suitable rust inhibitor.

All sections above 100 ft. have exposed raw metal and will rust

1st Platform view down

Top Platform view down

Guy cable systems:

1. Each anchor rod and spreader plate had rust removed and reconditioned with cold galvanized paint

2. Our engineer together with the assistance of our climber crew performed guy tension measurements on all guy cables

3. Guy anchor points were measured, the data entered in a structural analysis software program.

This program develops a theoretical analysis of the tower’s structural integrity, refer to appendix A for the resulting analysis.

4. The team also measured the straightness and calculated the tower twist at each guy elevation entering the data in the program for evaluation

5. The guy cable at the first elevation of the south guy lane is badly rusted, our recommendation is to replace this guy wire soon

6. The guy wire assemblies are not properly articulated at both ends, we would recommend to supply and install shackles at the ends of the guy wires.

Badly rusted guy cable

Antenna & transmission line systems:

1. Multiple abandoned and “ungrounded” transmission lines. These coax cables have been cut off at the base of the tower and abandoned in place. While this practice is both unsightly and contrary to government installation procedures, this action leaves the line ungrounded. The lightning strike energy will seek to lowest path to earth and with no path will ride along the line until it is inductively coupled to an adjacent grounded line. This induced current can conceivably couple into the center conductor of the active line and ride the line directly to the equipment.

Cutoff and ungrounded cables

2. This photo shows a compression in the coax line that appears to be the result of over tightening the plastic cable tie. This compression Will cause significant signal power to be reflected towards the source. If the source equipment is a transmitter, this power can and in most cases damage the output amplifier.

a. Solution is the replacement of this coax as this compression cannot be corrected.

b. An alternative option is to cut the coax and discard the damaged section and install back to back connectors.

c. The downside of this alternative will be a degraded line that will exhibit a higher reflected power level.

d. Our recommendation is to replace the coax line.

3. Antennas and mounts:

a. Several antennas are inactive and should be removed to reduce tower loading.

b. Antenna mounts at all locations have unacceptable levels of corrosion that require immediate attention to prevent total mount failure and creating a safety hazard to ground personnel.

c. In addition, the corroded mount hardware permits the migration of corrosion into the tower legs developing a weak point in the structure steel.

d. Active antennas have significant damage that have or will degrade service as seen in the photo

e. In photo below Omni in same azimuth as dipole with mounts touching each other. The wind will bang these antennas causing interference. In addition, the Omni is radiating into the dipole mast creating a reflection and degrading service.

Radome destroyed Mounts touching

U bolt and mount beyond re-condition

4. Transmission lines are routed and secured improperly per USAF standards. The existing coax cables are bundled and secured with wire to the tower legs. The insulation on this wire over the years has deteriorated and fallen off the wire leaving bare wire exposed. The wires are now rusted, this corrosion has penetrated through the paint and galvanizing and is corroding the tower steel.

5. Our recommendation is to remove these hanger wires, recondition the leg area and secure the coax using the proper coax hanger system.

6. Due to the improper installation of the transmission lines and noted damages, we recommend each line be tested to determine reflected power levels (return loss).

7. Measurement procedure:

a. Method #1 uses the antennas as the loads

b. Method #2 uses a calibration load to terminate the coax versus the antenna

c. There are obvious advantages with both procedures with the most accurate and recommended procedure being #2. This is the best of the two because it separates the antennas and lines for individual evaluation and analysis

d. The positive to method #1 is no climber is required. However, without having data from method two there is no baseline to compare in the future.

The above photo shows the kinked coax on the flange, this fault will be seen in a line sweep test and does create a reflection point back toward the transmitter thereby reducing the output power level and overheating the output amplifier.

The installation of the transmission lines on this tower follow no known practice. There is no hanger system and when the lines are secured, the installer used wire. The wire was initially insulated however, in time this insulation has deteriorated leaving bare wire to rust and corrode the tower leg.

Cable tie kinking the coax

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Calculated Values

Table 1 Tower Verticality and Straightness

Reference Elevation

Deviation along Axis 1

Deviation along Axis 2

Verticality Straightness Resultant Deviation

Allowable Resultant Deviation

Resultant Deviation between

Elevations

Allowable Deviation between

Elevations ft in in in in in in

385.00 2.49 -2.40 3.46 11.55

1.50 1.80

325.00 2.07 -0.96 2.29 9.75

0.41 2.40

245.00 1.66 -0.96 1.92 7.35

1.46 2.40

165.00 0.83 0.24 0.86 4.95

1.10 2.40

85.00 -0.24 0.00 0.24 2.55

0.24 2.55

0.00 0.00 0.00 0.00 0.00

Table 2 Tower Twist

Reference Elevation

Twist w.r.t Base Allowable Twist w.r.t Base

Relative Twist between Reference

Elevations

Allowable Twist between Reference

Elevations ft degrees +/- degrees degrees +/- degrees

385.00 2.90 5.00

2.61 3.00

325.00 0.29 5.00

0.87 4.00

245.00 1.16 5.00

0.58 4.00

165.00 0.58 5.00

0.29 4.00

85.00 0.29 4.25

0.29 4.25

0.00 0.00 0.00

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Table 3 Measured Guy Tensions Anchor

Location

ID

Guy Elevation at Tower

Guy Size and Type

Measured Tension at 80 F

Measured Tension adjusted to 60 F

Design Initial Tension at

60 F

Range of Tensions

Allowable ft kips kips kips kips

C3 385.00 9/16'' EHS 3.07 3.28 3.50 3.15 - 3.85

385.00 9/16'' EHS 3.08 3.29 3.50 3.15 - 3.85

385.00 9/16'' EHS 2.98 3.17 3.50 3.15 - 3.85

B3 385.00 9/16'' EHS 3.00 3.20 3.50 3.15 - 3.85

385.00 9/16'' EHS 3.00 3.21 3.50 3.15 - 3.85

385.00 9/16'' EHS 3.04 3.23 3.50 3.15 - 3.85

A3 385.00 9/16'' EHS 2.99 3.18 3.50 3.15 - 3.85

385.00 9/16'' EHS 3.19 3.40 3.50 3.15 - 3.85

385.00 9/16'' EHS 3.01 3.20 3.50 3.15 - 3.85

C2 325.00 5/8'' EHS 3.74 4.03 4.30 3.87 - 4.73

B2 325.00 5/8'' EHS 4.08 4.36 4.30 3.87 - 4.73

A2 325.00 5/8'' EHS 3.71 4.00 4.30 3.87 - 4.73

C2 245.00 9/16'' EHS 2.95 3.26 3.50 3.15 - 3.85

B2 245.00 9/16'' EHS 2.95 3.25 3.50 3.15 - 3.85

A2 245.00 9/16'' EHS 2.94 3.26 3.50 3.15 - 3.85

C1 165.00 9/16'' EHS 3.27 3.51 3.50 3.15 - 3.85

B1 165.00 9/16'' EHS 3.11 3.36 3.50 3.15 - 3.85

A1 165.00 9/16'' EHS 3.00 3.26 3.50 3.15 - 3.85

C1 85.00 9/16'' EHS 2.79 3.19 3.50 3.15 - 3.85

B1 85.00 9/16'' EHS 2.85 3.24 3.50 3.15 - 3.85

A1 85.00 9/16'' EHS 2.97 3.40 3.50 3.15 - 3.85

Table 4 Measured Guy Tensions - Average by Guy Level

Guy Elevation at Tower

Measured Tension at

80 F

Measured Tension adjusted to 60 F

Design Initial

Tension at 60 F

Range of Tensions

Allowable ft kips kips kips kips

385.00 3.04 3.24 3.50 3.15 - 3.85

325.00 3.84 4.13 4.30 3.87 - 4.73

245.00 2.95 3.26 3.50 3.15 - 3.85

165.00 3.13 3.38 3.50 3.15 - 3.85

85.00 2.87 3.28 3.50 3.15 - 3.85