ISO 20683-1:2016

INTERNATIONAL ISO
STANDARD 20683-1
Second edition
2016-08-15
Aircraft ground equipment — Nose
gear towbarless towing vehicle (TLTV)
— Design, testing and maintenance
requirements —
Part 1:
Main line aircraft
Matériels au sol pour aéronefs — Tracteur sans barre (TLTV) de train
avant — Exigences de conception, essais et entretien —
Partie 1: Aéronefs de ligne
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Design requirements . 4
4.1 General . 4
4.2 Towing loads . 4
4.3 Pick-up and holding system . 5
4.4 Oversteering protection . 5
4.5 Nose wheels retention . 6
4.6 Safety . 6
4.6.1 General. 6
4.6.2 Pick-up, release and associated loads . 6
4.6.3 Acceleration, deceleration and associated loads . . 6
4.6.4 Emergency braking . 7
4.6.5 Oversteer limits . 7
4.6.6 Oversteer alerting and/or protection . 7
4.7 Testing operations. 8
4.7.1 Snubbing and jerking . 8
4.7.2 Vibrations . 8
4.7.3 Aircraft braking . 8
4.7.4 Stability . 8
4.8 Nose gear steering angle limit . 9
4.9 Vehicle classification . 9
4.10 Placarding . 9
5 Testing requirements . 9
5.1 General . 9
5.2 Testing objectives . 9
5.3 Aircraft configuration .10
5.4 Calibration .10
5.4.1 General.10
5.4.2 Aircraft calibration .10
5.4.3 TLTV calibration .13
5.4.4 Oversteering calibration .14
5.5 Testing procedures .14
5.5.1 General.14
5.5.2 Data recording .14
6 Evaluation .15
6.1 Evaluation criteria .15
6.2 Normal condition testing .15
6.2.1 Testing methods .15
6.2.2 Tests number . .15
6.2.3 Pushback .15
6.2.4 Maintenance towing.16
6.2.5 Pick-up and release .16
6.2.6 Test evaluation .16
6.3 Stability testing .17
6.4 Extreme condition testing .17
6.4.1 Testing methods .17
6.4.2 Static load tests .17
6.4.3 Maximum acceleration and braking .17
6.5 Oversteer testing .18
7 Maintenance .18
7.1 General .18
7.2 Maintenance manual .19
7.3 Requirements .19
7.4 Calibration .20
7.5 Special tools .20
7.6 Training .20
7.7 Maintenance records .20
8 Quality control .21
9 Traceability and accountability .22
10 Modifications .22
11 Operating instructions .23
Bibliography .24
iv © ISO 2016 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 9, Air cargo and ground equipment.
This second edition cancels and replaces the first edition (ISO 20683-1:2005), which has been
technically revised.
A list of all parts in the ISO 20683 series can be found on the ISO website.
Introduction
This document specifies design, testing, maintenance and associated requirements to be applied on
towbarless aircraft towing vehicles to be used on main line civil transport aircraft in order to ensure
their operation cannot result in damage to aircraft nose landing gears, their steering systems, or
associated aircraft structure.
Throughout this document, the minimum essential criteria are identified by the use of the key word
“shall”. Other recommended criteria are identified by the use of the key word “should” and, while not
mandatory, are considered to be of primary importance in providing safe and serviceable towbarless
tractors. Alternative solutions may be adopted only after careful consideration, extensive testing and
thorough service evaluation have shown them to be equivalent.
vi © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 20683-1:2016(E)
Aircraft ground equipment — Nose gear towbarless
towing vehicle (TLTV) — Design, testing and maintenance
requirements —
Part 1:
Main line aircraft
1 Scope
This document is applicable to towbarless aircraft towing vehicles (TLTVs) interfacing with the
nose landing gear of main line civil transport aircraft with a maximum ramp mass over 50 000 kg
(110 000 lb). The requirements for regional transport aircraft with a lower maximum ramp mass are
specified in ISO 20683-2. It is not applicable to TLTVs which were manufactured before its date of
publication.
It specifies general design requirements, testing and evaluation requirements, maintenance, calibration,
documentation, records, tracing and accountability requirements in order to ensure that the loads
induced by the tow vehicle will not exceed the design loads of the nose gear or its steering system,
or reduce the certified safe life limit of the nose gear, or induce a stability problem during aircraft
pushback and/or gate relocation or maintenance towing operations.
This document specifies requirements and procedures for towbarless tow vehicles (TLTVs) intended
for aircraft pushback and gate relocation or maintenance towing only. It is not intended to allow for
dispatch (operational) towing (see Clause 3). Dispatch towing imposes greater loads on nose gears and
aircraft structure due to the combination of speed and additional passenger, cargo, and fuel loads.
This document does not apply to towbarless towing vehicles interfacing with aircraft main landing gear.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
Federal Aviation Regulations (FAR) 14 CFR Part 25, Airworthiness Standards: Transport category
1)
airplanes, paragraphs 25.301, Loads, and 25.509, Towing loads.
Certification Specifications and Acceptable Means of Compliance for Large Aeroplanes CS-25,
2)
paragraphs 25.301, Loads, 25.509, Towing loads, 25.745(d), Nose-wheel steering, and AMC 25.745(d).
ISO 6966-1, Aircraft ground equipment — Basic requirements — Part 1: General design requirements
ISO 6966-2, Aircraft ground equipment — Basic requirements — Part 2: Safety requirements
1) FAR Part 25 constitute the U.S.A. Government transport aircraft airworthiness Regulations, and can be obtained
from: US Government Printing Office, Mail Stop SSOP, Washington DC 20402-9328, U.S.A.
2) EASA CS25 constitute the European Governments transport aircraft airworthiness Regulations, and can be
obtained from: European Aviation Safety Agency: Ottoplatz 1, D-50679 Cologne, Germany - http://easa.europa.
eu/official-publication/.
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
main line aircraft
civil passenger and/or freight transport aircraft with a maximum ramp mass (3.3) over 50 000 kg
(110 000 lb)
3.2
regional aircraft
civil passenger and/or freight transport aircraft with a maximum ramp mass (3.3) between 10 000 kg
(22 000 lb) and 50 000 kg (110 000 lb)
3.3
maximum ramp mass
maximum ramp weight
MRW
maximum mass allowable for an aircraft type when leaving its parking position either under its own
power or towed, comprising maximum structural take-off mass (MTOW) and taxiing fuel allowance
3.4
pushback
moving a fully loaded aircraft [up to maximum ramp mass (3.3) (MRW)] from the parking position to the
taxiway. movement includes pick-up, push back with turn, a stop, a short push or tow to align aircraft
and nose wheels, and release
Note 1 to entry: Engines may or may not be operating. Aircraft movement is similar to a conventional pushback
-1
operation with a tow bar. Typical speed does not exceed 10 km/h (6 mph).
3.5
maintenance towing
movement of an aircraft for maintenance/remote parking purposes (e.g. from the parking position to a
maintenance hangar
Note 1 to entry: The aircraft is typically unloaded with minimal fuel load (reference light gross weight, LGW),
-1
with speeds up to 32 km/h (20 mph).
3.6
gate relocation towing
movement of an aircraft from one parking position to an adjacent one or one in the same general area
Note 1 to entry: The aircraft is typically unloaded with minimal fuel load (reference light gross weight, LGW),
with speeds intermediate between pushback and maintenance towing.
3.7
dispatch towing
operational towing
towing a revenue aircraft [loaded with passengers, fuel, and cargo up to maximum ramp mass (3.3)
(MRW)] from the terminal gate/remote parking area, to a location near the active runway, or conversely
-1
Note 1 to entry: The movement may cover several kilometres with speeds up to or over 32 km/h (20 mph), with
several starts, stops and turns. Replaces typical taxiing operations prior to takeoff or after landing.
2 © ISO 2016 – All rights reserved

Note 2 to entry: In the definitions of the towing modes, the frequency of operation has not been included. This
should not be interpreted to mean that no limitations are present. For limitations on the frequency of pushback
and maintenance operations, refer to the appropriate airframe manufacturer’s documentation or consult directly
with the airframe manufacturer.
3.8
towbarless towing vehicle
TLTV
towing vehicle acting without tow bar on an aircraft’s nose landing gear (3.9)
3.9
nose landing gear
NLG
aircraft nose landing gear in a tricycle landing gear layout
3.10
actual test gross weight
ATGW
reference aircraft mass for testing of the vehicle and aircraft, defined as the manufacturer’s operating
empty mass of the aircraft type concerned, plus fuel remaining in the tanks but lower than STGW
3.11
specified test gross weight
STGW
reference aircraft mass for testing of the vehicle and aircraft, defined as the manufacturer’s operating
empty mass of the aircraft concerned, plus at least 50 % of the maximum total fuel tanks capacity on
the type, or its equivalent in mass (payload may be accounted if present, providing aircraft balance
condition remains within limits)
3.12
maximum limits
limits (fore and aft tractive force, torsional, or angular) established by the airframe manufacturer as
not-to-exceed values intended to preclude possible damage to nose landing gear (3.9) or structure
Note 1 to entry: Maximum limits are established by airframe manufacturer’s documentation and may be different
for towbarless or tow bar towing operations. All aircraft load limits are limit loads as defined in FAR/EASA CS
paragraph 25.301 (a).
3.13
operational limits
limits (fore and aft tractive force, torsional, or angular) which are set at a lesser value than the maximum
limits (3.12) established by the airframe manufacturer
3.14
aircraft family
grouping of aircraft types or subtypes, defined by their manufacturer, for which the same maximum
limits (3.12) may be applied
Note 1 to entry: A family usually encompasses all sub-types of a given type, but may also include other types.
Testing for one (usually the lightest) model of the family results in towbarless towing approval for the whole
family. See airframe manufacturer’s towbarless towing evaluation documentation.
3.15
TLTV setting
grouping of aircraft types or sub-types, defined by the TLTV manufacturer, for which a single operational
limits (3.13) setting is used
Note 1 to entry: A single TLTV setting usually encompasses aircraft types or sub-types, which may be produced
by different airframe manufacturers, in a same defined MRW range.
3.16
drag load
tow force
total force from the tow vehicle on the nose gear tires in the “X” axis (3.17)
3.17
“X” axis
fore and aft axis of the tow vehicle, parallel to the ground
3.18
oversteer
exceedence of maximum torsional load or angular limits where potential damage to the nose landing
gear (3.9) structure or steering system could take place
Note 1 to entry: These limits are defined in the appropriate airframe manufacturer’s documentation. Torsional
load limits typically occur after exceeding angular limits, but may occur before the angular limit is reached (e.g.
nose gear hydraulic system bypass failure).
3.19
snubbing
sudden relief and reapplication of acceleration/deceleration loads while TLTV and aircraft are in motion
3.20
jerking
sudden application of push/pull forces from a complete stop
4 Design requirements
4.1 General
4.1.1 Towbarless tow vehicles (TLTVs) shall comply with the applicable general requirements of
ISO 6966-1.
4.1.2 Airframe manufacturers should provide information for each aircraft type which allows TLTV
manufacturers or airlines to self-test or evaluate the towbarless tow vehicles themselves.
Refer to the airframe manufacturer’s documentation for evaluation requirements and detailed testing
procedures that may be different from or additional to those contained in this document.
4.1.3 TLTV manufacturers should prepare and provide customers or regulatory agencies, as required,
with a certificate of compliance or equivalent documentation, as evidence that successful testing and
evaluation of a specific tow vehicle/aircraft type combination has been completed in accordance with
this document and/or the applicable airframe manufacturer’s documentation.
This certificate shall allow use of the vehicle on specifically designated aircraft models/types.
The certificate should be established under an appropriate quality control program meeting the
requirements of ISO 9001 or equivalent pertinent industry standard.
4.2 Towing loads
4.2.1 The push and pull towing forces induced by the TLTV onto the aircraft’s nose landing gear as a
result of either accelerating or braking shall be verified as per Clause 5 and/or Clause 6 hereafter, and
shall not at any time exceed the maximum values specified by the aircraft manufacturer.
4 © ISO 2016 – All rights reserved

4.2.2 Depending on the range of aircraft types the TLTV is compatible with, preset towing load values
may be used for a number of aircraft types or sub-types in a given MRW range.
In this case, each TLTV setting shall comply with the maximum limits specified by the manufacturer(s)
of the designated aircraft types, sub-types, or family(s) thereof as defined by the aircraft manufacturers,
and each TLTV setting shall be subjected to a separate verification.
4.3 Pick-up and holding system
4.3.1 The TLTV’s nose landing gear pick-up/release device should operate in a smooth and
continuous manner.
Abrupt or oscillating loads during the pick-up/release sequence should not occur. It should be
designed to minimize the loads during the pick-up/release sequence. The drag loads induced during
pick-up/release should fall well below the “peak” loads experienced during a typical operation.
4.3.2 The maximum loads induced by pick-up and release sequences shall be measured either on an
aircraft or on a fixture representative of the nose gear geometry.
The vertical load on the nose gear or fixture shall be equal to the vertical load used for fatigue
justification (refer to the appropriate airframe manufacturer’s documentation). The maximum
lift (height above the ground) of the nose gear shall not exceed the values given in the airframe
manufacturer’s documentation if such values are provided.
4.4 Oversteering protection
4.4.1 The maximum angular or torsional load limits stated by the aircraft’s manufacturer in the event
of oversteering shall not at any time be exceeded.
See aircraft manufacturer’s TLTV assessment criteria document.
4.4.2 This may be achieved either by oversteer protection built into the TLTV, or by an oversteer
alerting system being provided.
4.4.3 Oversteer protection may be achieved either by intrinsic design precluding the possibility of
either limit being reached or exceeded or by a fail-safe oversteer protection system ensuring they shall
not be exceeded.
Oversteer alerting shall consist in an appropriate fail-safe warning system installed on the TLTV,
providing the driver with unmistakable indication that one of the maximum limits was reached.
4.4.4 No testing of the TLTV oversteer protection or alerting systems shall be performed on an in-
service aircraft, in order to preclude any possible damage to the NLG structure or steering system.
Such testing should be accomplished with a suitable ground testing device representative of the
specific aircraft model for which the TLTV is intended or through appropriate numeric simulation
demonstration.
EASA CS requirements:
For aircraft registered or operated under EASA CS-25 paragraph 25.745(d) and associated AMC 25.745(d),
requires the TLTV manufacturers to provide a Declaration of Compliance (see 4.1.3) of their unit’s
oversteer protection or oversteer alerting system(s) with the present International Standard and the
criteria published by the manufacturer of each aircraft type for which it is intended, and the aircraft
manufacturers to list in their appropriate documentation the TLTV models that were specifically
accepted for each aircraft type based on this Declaration of Compliance.
4.5 Nose wheels retention
4.5.1 The nose wheels shall be held by the vehicle in such a way that pitch-up of the aircraft shall not
cause the wheel to disengage from the pick-up device at any nose gear steering angle.
A positive wheel retaining feature shall be provided. If the nose gear is “canted”, a turning maneuver
will cause uneven loading on the nose gear (i.e. for an aft canted gear, the vertical load on the inboard
nose wheel will tend to increase and conversely, the vertical load on the outboard nose wheel will
tend to decrease). The retention feature shall allow for uneven tire displacement without imposing
additional loads on the nose gear.
4.5.2 The geometry of the holding device shall be such that no interference with aircraft structure may
occur (e.g. torque links, weight and balance sensors, tires, water spray deflector, etc.) at all wheel steering
angles up to the limits defined by the airframe manufacturer’s documentation, and the full range of shock
strut extensions and tire deflections.
Surface contact area between pick-up device and tire surface should be sufficient to preclude
unacceptable tire loading (refer to tire manufacturer for bearing pressure specifications).
4.6 Safety
4.6.1 General
Towbarless tow vehicles (TLTVs) shall comply with the applicable safety requirements of ISO 6966-2.
4.6.2 Pick-up, release and associated loads
4.6.2.1 During the loading sequence, safety equipment shall inhibit any movement of the loading
device if the nose wheel is not properly positioned.
Positive clamping and correct positioning of the nose wheel shall be ensured.
4.6.2.2 When the positioning pick-up/release sequence involves a relative motion between the vehicle
and the aircraft, only the vehicle shall be allowed to move (see 4.2).
The aircraft parking brake should be applied or wheels properly chocked during this phase. TLTV
design shall ensure that no loads higher than authorized are applied to the aircraft.
4.6.2.3 In order to avoid damage to the aircraft, the net load from all points of contact between the vehicle
and nose gear tires shall be limited (on “X” axis) at a value lower than or equal to the operational limit.
Any single failure of the tow vehicle’s load limiting system shall not cause loads which exceed the
maximum limits.
4.6.2.4 If the pick-up/release sequences are fully automatic, an emergency stop or deadman switch
shall allow the operator to freeze the sequence at any time.
An automatic or manual system shall allow reversal of the sequence and restore the starting position.
4.6.2.5 If aircraft type selection is necessary prior to the pick-up or towing/pushback sequence, a
safety system in the vehicle shall inhibit further operation if the incorrect aircraft type is selected.
4.6.3 Acceleration, deceleration and associated loads
4.6.3.1 If towing is attempted while aircraft brakes are applied or wheel chocks are in place, a safety
device on the TLTV shall limit the maximum static force to the safety limit as defined in 4.6.3.2 a).
6 © ISO 2016 – All rights reserved

4.6.3.2 The vehicle’s maximum pulling and braking forces shall be limited to the maximum permissible
nose landing gear loads of the aircraft (see airframe manufacturer’s documentation and FAR/EASA CS
paragraph 25.509).
One or two limiters shall be used.
a) A primary maximum load limiter, designed to the maximum load limits specified by the airframe
manufacturer, shall be installed to limit the loads applied to the nose gear during all operations. It
shall not be possible to override the limiter. Any activation of the maximum load limiter constitutes
a recordable event.
b) A secondary operational load limiter, designed to lower operational loads, may be installed. If
installed, whenever operational limits during acceleration or deceleration are exceeded, a safety
system shall inhibit the further loading effort of the vehicle (engine back to idle or gear box to
neutral without braking of the vehicle). The safety system shall allow resetting only when the
vehicle is stopped. No record of the event is necessary.
4.6.3.3 Control of the loads may be based either on a limitation of the acceleration/ deceleration or
on a limitation of the tow force/brake force. It may also be possible to control tow forces by controlling
acceleration/deceleration.
4.6.4 Emergency braking
If an emergency braking system is incorporated or installed in the TLTV, the braking or decelerating
load shall not exceed the maximum allowable nose landing gear limits, but it may exceed the operational
limits. Emergency braking activation shall be well protected against inadvertent triggering.
4.6.5 Oversteer limits
4.6.5.1 Oversteer angular and torsional limits are not to be exceeded. Oversteer testing should not be
performed on the aircraft.
4.6.5.2 For European registered or operated aircraft, the EASA CS-25 [CS 25.745(d)] require oversteer
alert or protection systems on the aircraft or the TLTV (see 4.6.6). If a TLTV is designed to meet EASA CS-
25 requirements, then testing to demonstrate vehicle oversteer limit alerting or protection functionality
should be performed by the TLTV manufacturer in a suitable test facility or rig. TLTV manufacturers
or airplane operators should consult with the airframe manufacturer or local aviation regulatory
authorities, as appropriate, for current regulation status.
4.6.5.3 The maximum steering angle for conventional tow bar towing, as listed in the airframe
manufacturer’s documentation, is applicable for nose gear towbarless towing, unless otherwise noted.
Airframe manufacturers may establish different maximum steering limits between conventional tow
bar and towbarless towing due to the absence of shear protection provided by traditional tow bar
connections.
4.6.6 Oversteer alerting and/or protection
4.6.6.1 The tractor shall be equipped with a fail-safe oversteer alerting/indication or protection
system that
a) activates an in-cab (red) warning light and audible alarm to indicate the maximum safety limit has
been reached, and
b) requires a specific recordable action to complete the pushback/towing operation, in order to
make it unmistakable to the tow vehicle driver that an inspection of the nose landing gear by an
authorized engineer shall be initiated.
4.6.6.2 In addition, it is desirable that the device activates an in-cab (amber) warning light and audible
signal to indicate an operational limit has been reached. The oversteer indication system shall allow
sufficient time for the tow vehicle operator to take appropriate action to avoid reaching a safety limit.
4.6.6.3 The system shall be automatically activated when the airplane is coupled to the tow vehicle.
4.6.6.4 The oversteer indication and/or protection system shall be designed to protect the range of
aircraft types that can be handled by the tow vehicle.
Oversteer is defined as exceeding maximum allowable steering angle or torsional load.
4.6.6.5 An optional system may provide a structural fuse (or other reliable load limiting system) on the
tow vehicle which will prevent the application of torsional loads on the nose landing gear that exceeds
the airframe manufacturer’s specified maximum limit.
4.7 Testing operations
4.7.1 Snubbing and jerking
Snubbing and jerking effects or movements should be avoided during testing.
4.7.2 Vibrations
If severe or abnormal vibrations occur, testing should be discontinued and the cause determined.
4.7.3 Aircraft braking
The aircraft brakes should not be used while the aircraft is being towed by a TLTV, except in an
emergency situation. Aircraft braking, while the aircraft is under tow, may result in loads exceeding
the aircraft’s design loads and may result in structural damage and/or nose gear collapse. For these
reasons, it is recommended that airlines take appropriate steps to preclude aircraft braking during
normal towbarless towing. The carrier’s or airframe manufacturer’s maintenance manual and
operational procedures shall be complied with.
4.7.4 Stability
4.7.4.1 Attention shall be paid to aircraft stability. Stability may be affected by aircraft type, mass, centre
of gravity location, weather condition, runway roughness, and slope. Stability shall be demonstrated by
tests in accordance with the airframe manufacturer documentation.
4.7.4.2 The testing shall be conducted under maximum speed capability of the vehicle.
4.7.4.3 If a lateral instability is detected, a margin of 5 km/h (3 mph) shall be maintained between the
speed at the beginning of instability and the maximum towing speed.
4.7.4.4 With minimal static load on the nose landing gear sufficient to move the airplane, no pitch
oscillation of the aircraft shall occur, such that it would extend the shock absorber beyond the allowable
strut extension in the ground mode.
4.7.4.5 Proper operational procedures shall be defined and followed to ensure vehicle and airplane
stability.
8 © ISO 2016 – All rights reserved

4.8 Nose gear steering angle limit
The maximum steering angle for conventional tow bar towing, as specified in the airframe
manufacturer’s documentation, is applicable for nose gear towbarless towing, unless otherwise noted.
4.9 Vehicle classification
The TLTV model shall be classified according to its intended use, and tested accordingly, as either
a) category I: pushback only, or
b) category II: maintenance towing only, or
c) category III: both pushback and maintenance.
4.10 Placarding
Limitations and warnings imposed by all conditions shall be placarded in a location readily visible to
the tow vehicle driver, including but not necessarily limited to the following:
a) classification category defined in 4.9;
b) types of aircraft the TLTV is qualified for (by TLTV setting if applicable);
c) maximum allowable speed;
d) maximum allowable towing angle, etc.
5 Testing requirements
5.1 General
5.1.1 No testing with an aircraft shall be performed if any requirement in Clause 4 is not met.
5.1.2 In case of a vehicle for which only partial qualification is required (e.g. pushback only), the tests
performed shall be appropriate to its category classification per 4.7.
5.1.3 Dynamic numeric simulation may be used instead of the specified tests, unless prohibited by
airframe manufacturer’s documentation, and providing it guarantees at least equivalent results reliability.
5.2 Testing objectives
a) To measure the maximum values of the loads introduced into the airframe during extreme
conditions, such as maximum acceleration and braking.
b) To verify that potential oversteer does not exceed the airframe manufacturer’s specified limits.
Also, to verify/demonstrate the capability of the TLTV to recognize steering angle or torsional
load limits and to alert the vehicle operator accordingly. However, because of the potential for
damage, no actual testing with an aircraft shall be performed for oversteer indication or protection
calibration.
c) To verify the stability of the tow vehicle/aircraft combination throughout the total range of
operational speeds.
d) To evaluate the fatigue loads introduced into the airframe by normal utilization of the vehicle
during the specific category of operations for which qualification is intended.
5.3 Aircraft configuration
5.3.1 Before any calibration or testing is accomplished, all landing gear shall be properly serviced as
defined by the airframe manufacturer’s instructions.
5.3.2 Aircraft weights, light and heavy gross weight and C.G. position for testing shall be in accordance
with the requirements in the calibration and test requirements (see 5.4 and 5.5) and the airframe
manufacturer’s documentation.
The airframe manufacturer (see Bibliography) should be consulted for any deviation from documented
weights.
5.3.3 The aircraft shall be in the correct towing configuration as defined by the airframe manufacturer’s
maintenance and operational documentation.
5.4 Calibration
5.4.1 General
5.4.1.1 Tests may be performed with an instrumented aircraft or an instrumented towing vehicle.
Calibration of both are discussed in this clause (see 5.5.1 for restrictions in the use of instrumented
vehicles).
5.4.1.2 To measure fore and aft tow loads on the nose landing gear, strain gauges shall be installed
at the nose gear locations (drag brace, torque arm, or other components) specified by the airframe
manufacturer.
Calibration of the strain gauges is accomplished by pushing and pulling the nose gear with known
tow loads.
5.4.1.3 To measure fore/aft and torsional tow loads on the TLTV, strain gauges shall be installed at
vehicle locations specified by the vehicle manufacturer and shall be calibrated to a known tow load input.
5.4.1.4 Once the strain gauges have been calibrated, the aircraft can be towed with the TLTV and the
tow loads can be determined directly from the strain measurements.
The following proced
...