ISO 20683-1:2016

DRAFT INTERNATIONAL STANDARD
ISO/DIS 20683-1
ISO/TC 20/SC 9 Secretariat: AFNOR
Voting begins on: Voting terminates on:
2015-11-05
2016-02-05
Aircraft ground equipment — Design, test and
maintenance for towbarless towing vehicles (TLTV)
interfaced with nose-landing gear —
Part 1:
Main-line aircraft
Matériels au sol pour aéronefs — Conception, essais et entretien des tracteurs sans barre (TLTV)
s’accouplant au train d’atterissage avant —
Partie 1: Aéronefs de ligne
ICS: 49.100
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 20683-1:2015(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2015

ISO/DIS 20683-1:2015(E) ISO/FDIS 20683-1:2015(E)

Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Design requirements . 4
4.1 General . 4
4.2 Towing loads . 5
4.3 Pick-up and holding system . 5
4.4 Oversteering protection . 5
4.5 Nose wheels retention . 5
4.6 Safety . 6
4.7 Testing operations . 8
4.8 Nose gear steering angle limit . 8
4.9 Vehicle classification . 8
4.10 Placarding . 8
5 Testing requirements . 9
5.1 General . 9
5.2 Testing objectives . 9
5.3 Aircraft configuration . 9
5.4 Calibration . 10
5.5 Testing procedures . 14
6 Evaluation. 15
6.1 Evaluation criteria . 15
6.2 Normal condition testing . 15
6.3 Stability testing . 17
6.4 Extreme condition testing . 17
6.5 Oversteer testing . 19
7 Maintenance . 19
7.1 General . 19
7.2 Maintenance manual . 20
7.3 Requirements . 20
7.4 Calibration . 20
7.5 Special tools . 21
7.6 Training. 21
7.7 M aintenance record s . 21
8 Quality control . 22
9 Traceability and accountability . 22
10 Modifications . 23
11 Operating instructions . 23
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved
ISO/FDIS 20683-1:2015(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Design requirements . 4
4.1 General . 4
4.2 Towing loads . 5
4.3 Pick-up and holding system . 5
4.4 Oversteering protection . 5
4.5 Nose wheels retention . 5
4.6 Safety . 6
4.7 Testing operations . 8
4.8 Nose gear steering angle limit . 8
4.9 Vehicle classification . 8
4.10 Placarding . 8
5 Testing requirements . 9
5.1 General . 9
5.2 Testing objectives . 9
5.3 Aircraft configuration . 9
5.4 Calibration . 10
5.5 Testing procedures . 14
6 Evaluation. 15
6.1 Evaluation criteria . 15
6.2 Normal condition testing . 15
6.3 Stability testing . 17
6.4 Extreme condition testing . 17
6.5 Oversteer testing . 19
7 Maintenance . 19
7.1 General . 19
7.2 Maintenance manual . 20
7.3 Requirements . 20
7.4 Calibration . 20
7.5 Special tools . 21
7.6 Training. 21
7.7 Maintenance records . 21
8 Quality control . 22
9 Traceability and accountability . 22
10 Modifications . 23
11 Operating instructions . 23

ISO/FDIS 20683-1:2015(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 20683-1 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 9, Air cargo and ground equipment.
This second/third/. edition cancels and replaces the first/second/. edition (), [clause(s) / subclause(s) /
table(s) / figure(s) / annex(es)] of which [has / have] been technically revised.
ISO 20683 consists of the following parts, under the general title Aircraft ground equipment — Nose gear
towbarless towing vehicle (TLTV) - Design, testing and maintenance requirements:
 Part 1: Main line aircraft
 Part [n]:
 Part [n+1]:
 Part 1: Main line aircraft
 Part 2 : Regional aircraft
iv © ISO 2015 – All rights reserved

ISO/FDIS 20683-1:2015(E)
Introduction
This International Standard, constituting Part 1 of International Standard ISO 20683, Aircraft ground
equipment — Nose gear towbarless towing vehicles (TLTV) — Design, testing and maintenance requirements,
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 International Standard, 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.
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 20683-1:2015(E)

Aircraft ground equipment — Nose gear towbarless towing
vehicle (TLTV) - Design, testing and maintenance
requirements — Part 1: Main line aircraft
1 Scope
This International Standard 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 (Part 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 International Standard specifies requirements and procedures for towbarless tow vehicles (TLTVs)
intended for aircraft push-back and gate relocation or maintenance towing only. It is not intended to allow for
dispatch (operational) towing (see clause 3, Terms and definitions). 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 International Standard does not apply to towbarless towing vehicles interfacing with aircraft main landing
gear.
2 Normative references
The following referenced documents are indispensable for the application 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 airplanes,
1)
paragraphs 25.301, Loads, and 25.509, Towing loads .
Certification Specifications and Acceptable Means of Compliance for Large Aeroplanes CS-25, paragraphs
2)
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 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/.
ISO/FDIS 20683-1:2015(E)
ISO 6966-2, Aircraft ground equipment — Basic requirements — Part 2 : Safety requirements.
NOTE Also see informative references in Bibliography.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
main line aircraft
civil passenger and/or freight transport aircraft with a maximum ramp mass over 50 000 kg (110 000 lb)
3.2
regional aircraft
civil passenger and/or freight transport aircraft with a maximum ramp mass between 10 000 kg (22 000 lb)
and 50 000 kg (110 000 lb)
3.3
maximum ramp mass
MRW
Maximum Ramp Weight
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
push back
moving a fully loaded aircraft (up to maximum ramp mass (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. Engines may or may not be operating. Aircraft movement is similar to a conventional push back
-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). The aircraft is typically unloaded with minimal fuel load (reference light gross weight,
-1
LGW), 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. The
aircraft is typically unloaded with minimal fuel load (reference light gross weight, LGW), with speeds
intermediate between push back and maintenance towing
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ISO/FDIS 20683-1:2015(E)
3.7
dispatch towing
operational towing
towing a revenue aircraft (loaded with passengers, fuel, and cargo up to maximum ramp mass (MRW)), from
the terminal gate/remote parking area, to a location near the active runway, or conversely. The movement
-1
may cover several kilometers 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
NOTE 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 push-back 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
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 or structure
NOTE 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/JAR 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
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 may
be applied
NOTE 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
manufacturers towbarless towing evaluation documentation.
ISO/FDIS 20683-1:2015(E)
3.15
TLTV setting
grouping of aircraft types or sub-types, defined by the TLTV manufacturer, for which a single operational limits
setting is used
NOTE 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
"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
structure or steering system could take place
NOTE 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 International Standard.
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 International
Standard and/or the applicable airframe manufacturer’s documentation. This certification 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 (see Bibliography) or equivalent
pertinent industry standard.
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ISO/FDIS 20683-1:2015(E)
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 clauses 5 and/or 6 hereafter, and shall not at any time
exceed the maximum values specified by the aircraft manufacturer.
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
4.2.1 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.
4.2.2 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.
NOTE 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 clause 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 must be provided. If the nose gear is "canted", a turning maneuver will cause uneven loading on the
ISO/FDIS 20683-1:2015(E)
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 must
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 clause 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 pickup/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 pickup or towing/push-back 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 clause 4.4.3.2 a).
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.
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ISO/FDIS 20683-1:2015(E)
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 clause 4.4.6). 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 must 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 exceed the
airframe manufacturer’s specified maximum limit.
ISO/FDIS 20683-1:2015(E)
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, center
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.
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:
8 © ISO 2015 – All rights reserved

ISO/FDIS 20683-1:2015(E)
a) classification category defined in clause 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 clause 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 must 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 clauses 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.
ISO/FDIS 20683-1:2015(E)
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 clause 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 must 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 must be installed at
vehicle locations specified by the vehicle manufacturer and must be calibrated to a known tow load input.
5.4.1.4 Once the strain gauges have been cal
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