Incidents have occurred at certain airports where the in-pavement light fixture bolted connections have failed resulting in light fixtures completely separating from the light bases or light base extensions. Loose, missing, or broken bolts place more stress on the surrounding bolts in the bolt circle. This can lead to damage of the light base or light fixture and may lead to the complete failure of the remaining bolts, creating a potential hazard for aircraft

1. Current Bolt Problems: A Review
Jaquith Industries Inc.

2. Current Bolt Problems
Incidents have occurred at certain airports where the
in-pavement light fixture bolted connections have
failed resulting in light fixtures completely separating
from the light bases or light base extensions
After these incidents, the FAA directed airports to
inspect AGL units: FAA Part 139 CertAlert No. 14-03
Resulting Inspections
Inspections at multiple airports showed similar problems
Missing Bolts - Broken Bolts – Missing Lock Washers
Improperly Torqued Bolts – Loose Fixtures etc.
Missing Lock WasherMissing Lock Washer
Loose BoltsLoose Bolts
Jaquith Industries Inc.

3. Current Bolt Problems
Loose, missing, or broken bolts place more stress on the surrounding bolts in the
bolt circle. This can lead to damage of the light base or light fixture and may lead to
the complete failure of the remaining bolts, creating a potential hazard for aircraft
Possible Root Causes
•Inadequate clamping forces to resist shear forces
generated by modern commercial aircraft
•Improper installation & maintenance of the AGL
units
•Reduced maintenance intervals, due to the use of
LED fixtures
Jaquith Industries Inc.

4. Current FAA Bolt Guidance
Per EB-83
• A maximum of 185 in lbs. of torque for a dry 18-8 SS bolt is recommended
• A torque of less than 185 in. lbs. should be used for a SS 18-8 bolt with anti-seize
compound and for coated bolts
• In-pavement fixture bolts should be checked bi-monthly per AC150/5340-26C
• All bolts should be replaced after removal. Bolts should never be reused
• Always replace the two part locking washers every time the light fixture is removed from
the light base. Never use a split type locking washer
• Always clean the light base upper flange threaded holes before bolt installation
• Always clean the mating surfaces between the light base and the light fixture before
reinstallation
Jaquith Industries Inc.

5. FAA Testing of In-Pavement Light Fixtures
Future EB-83 Guidance
Jaquith Industries is currently consulting with the FAA & Intertek to conduct
comprehensive bolt testing and determine changes to EB-83
• Conduct Shear Force, Compressive Load, and Vibration Testing
to Evaluate Performance of Light Fixture Assemblies Based on
Increased Bolt Clamping Loads
• Determine Strength Limitations of Light Fixture Assemblies for
Resisting Increased Bolt Clamping Forces
• Instrument and Install In-Pavement Light Fixtures in Runway
and/or Taxiway to Evaluate Performance of Light Fixture
Assemblies under Controlled Aircraft Wheel Loading Conditions
• Utilize Instrumented B727 Aircraft and Smaller Size Aircraft to
Evaluate Light Fixture Assemblies Under Varying Wheel
Load/Tire Pressure Conditions
• Conduct Bolt Corrosion Testing per MIL-STD-810
Jaquith Industries Inc.

6. FAA Testing of In-Pavement Light Fixtures
Relationship of Shear Forces – Clamping Force - Tension-
Torque
What does it all mean?
Torqueing the bolts in the bolt circle of the light
fixture / light base creates tension (elongation
of the bolt) within the bolt. The tension in each
bolt combines to create a clamping force that
holds the light fixture to the light base and
works to resist the shearing forces placed on
the AGL unit during aircraft loading. These
shearing forces are greatest during aircraft
braking or turning.
Jaquith Industries Inc.

7. FAA Testing of In-Pavement Light Fixtures
EB-83 Horizontal Shear Forces
Shear Forces are generated as the result of an aircraft running overtop the light
fixture. These forces are the highest when an aircraft is braking or exiting the runway
using a high speed exit taxiway
Clamping forces must be sufficient to resist the
shearing forces exerted on the light fixture during
aircraft braking and high speed exits from the runway
FAA Currently Requires:
“The light fixture must withstand a shear load of
3,000 pounds (1,360.78 kg) applied to the top of the
light in any direction parallel to the mounting surface.”
The FAA will be conducting shear force testing to
evaluate shear forces present under various
conditions and determine clamping forces & bolt
torque needed to resist those shearing forces. We
expect the FAA to require the light fixture withstand
shearing forces greater than the current 3,000 lbs.
Jaquith Industries Inc.

8. The FAA will be conducting testing to
determine the required clamping force to
withstand higher shear forces placed on the
light fixture. The FAA will also determine
clamping forces generated at specific bolt
torque values with various bolts, sizes, &
materials. We expect the FAA to increase
recommended clamping forces to withstand
higher shear forces
FAA Testing of In-Pavement Light Fixtures
EB-83 Fixture & Bolt Clamping Forces
Required Fixture Clamping Force =
(Shear / K of Friction) x Safety Factor
Required Fixture Clamping Force =
(3,000 lbs. / .45) x 2
Required Fixture Clamping Force =
Approximately 13,400 lbs.
Required Clamping Force Per Bolt =
Fixture Clamping Force / # of Bolts
Required Clamping Force Per Bolt =
13,400 lbs. / 6 Bolts
Required Clamping Force Per Bolt =
Approximately 2,300 lbs.
Determining Required Clamping Forces
Clamping forces are the result of tension in the bolt. Clamping forces are generated by
the combined tension of each bolt in the bolt circle. Clamping forces must be sufficient to
resist the shearing forces exerted on the light fixture during aircraft braking or exiting the
runway using a high speed exit taxiway
Jaquith Industries Inc.

9. FAA Testing of In-Pavement Light Fixtures
EB-83 Torque vs Tension
Torque is the amount of effort required to thread the bolt into the top flange. While
tension refers to the elongation of the bolt that produces the clamping force to hold
the light fixture to the light base
The FAA will test several different bolts on
various light base assemblies to determine
the strength limits of various bolts & light
fixture assemblies
The Balancing Act:
It is important that the bolt tension
create a high enough clamping force
to resist shear forces. However we
must not create so much tension
that the threads of the bolt or flange
ring are damaged. It is important to
remember fluctuations in bolt
tension within a bolt circle may lead
to uneven bolt loading, which may
damage bolts, fixtures, and light
base flange
T = Torque
K = Coefficient of Friction
D = Bolt Diameter
Fp = Axial Tension
Jaquith Industries Inc.

10. FAA Testing of In-Pavement Light Fixtures
EB-83 Torque vs Tension
Torque is a relatively poor way of estimating clamping force because the
value for K can be greatly influenced by the friction present between the top
flange & bolt threads
Torque vs Tension with Changing K What Can Influence K (friction) Value?
•Damaged threads on the bolt or top flange
•Use of anti-seize or lubricant compounds
•Rust or elongation of the threads in bolts that have
been re-used
•Debris in the bolt or top flange threads
K = .20 K = .10
The FAA will test several different bolts on various light base assemblies to
determine K (friction) values. Values will serve as a baseline for calculating
required torque. We expect that the FAA will require higher torque values to
overcome fluctuations in the K value and produce higher clamping forces
Jaquith Industries Inc.

11. Bolt Recommendations
Grade 5 Coated Bolts
• Coefficient of friction .05 -.10 – Translates to higher
clamping force at lower torque
• Bolts already coated- no need to apply anti-seize
products like Loctite – More consistent K values
• Reduced risk of galling
• In the event of a “breakage” bolts are more easily
drilled out
• Grade 5 bolts are often stronger than stainless steel
bolts
Jaquith Industries Inc.

12. Alternative Bolt Recommendation
18-8 Stainless Steel Bolts with 51609 Loctite
• Stainless steel bolts have a proven ability to secure
the light fixture to the light base
• When used with 51609 heavy duty Loctite the
coefficient of friction is lowered – producing higher
clamping forces at lower toque
• Stainless steel bolts are cheaper in comparison to
coated bolts
Considerations:
• Stainless steel bolts have the potential to produce a
galling effect
• Even with the use of Loctite stainless steel bolts have
a higher coefficient of friction than coated bolts
Jaquith Industries Inc.

13. Bolt & Washer Recommendations
LOCK Washers
• Prevents vibration from loosening bolt and
decreasing clamping forces or creating
uneven clamping forces between the light
fixture and light base
• 2 piece washer “bites” bolt head and light
fixture – securing the bolt, washer and fixture
• Step cam between the 2 piece lock washers
prevents bolt from moving
• Lock washers should be changed every time
bolts are removed to protect the integrity of
the lock washer system
Jaquith Industries Inc.

14. Recommended Best Practices
Maintenance & Bolt Torque
• Ensure bolt & flange threads are clean and not damaged
• Ensure all mating surfaces are clean and free of debris
• Bolts should be torqued with a calibrated torque wrench
and never a high speed air impact wrench
• Bolts should be torqued to the bolt or light fixture
manufacturers reccomondations (ADB – 500 GBA – 300)
• “Dry” stainless steel bolts should never be used with a
stainless steel top ring due to the potential for galling
• Bolt torque should be checked on a regular basis with
emphasis on high stress or problem areas
• Replace bolts & lock washers after every use
• Should threads become damaged – they should be
repaired with Jaquith’s thread repair kit
Jaquith Industries Inc.