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MCD Booklet

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Early detection of transmission failures through oil system debris assessment
  • Early detection of transmission failures through oil system debris assessment

  • Important information

    The purpose of this document is to assist line maintenance personnel with oil system trouble-shootingfor the following engine/airframe types:

    RB211-22B Lockheed L1011 RB211-524 Boeing 747 and 767, Lockheed L1011 RB211-535 Boeing 757, Tupolev Tu-204 Trent 500 Airbus Industries A340-500/600 Electric MCD (E)MCD Trent 700 Airbus Industries A330-200/300 Trent 800 Boeing 777 BRR 710 Gulfstream GV

    Bombardier Global ExpressBAe Nimrod 2000

    BRR 715 Boeing 717 Tay Gulfstream GIV, Fokker 70, Fokker 100, Boeing 727 V2500 Airbus Industries A319, A320, A321, Boeing MD-90

    This document does not amend, replace or supersede any information contained in the respective AircraftMaintenance Manuals.

    All maintenance must be carried out in accordance with the relevant Aircraft Maintenance Manual.

  • 1Contents

    Summary 2

    Regular MCD inspection benefits 3

    MCD standard and configuration 4

    Diagnostic MCDs 7

    Bayonet MCD practices 9

    Screw-in MCDs practices 11

    Maintenance schedules and practices 12

    Multiple engine inspection 12

    MCD inspection intervals 12

    MCD inspection practices 13

    Method for MCD inspection 15

    Removal and examination 15

    Method for scavenge (fine) filter inspection 25

    Storage of debris 35

    Debris identification 36

    Bearing lapping failure producing fines 37

    Gear wear producing fines 38

    Bearing fatigue failure producing flakes 39

    Gear tooth fragments 40

    Chips 41

    Cage rivet failure 42

    Roller bearing cage tang failure 43

    Build debris or swarf 44

    Interpreting the results 45

    Actions to take when debris is discovered 46

  • 2Summary

    The early detection of transmissions failures can be achieved through

    regular inspection of the oil system Magnetic Chip Detectors (MCDs). This

    brochure has been developed to describe the best practices for Magnetic

    Chip Detector (MCD) inspection and debris assessment. Occasionally it may

    be necessary to confirm the debris findings on an MCD by inspection of the

    oil scavenge and pressure filters, which is also described. This brochure is

    intended for use by line maintenance and laboratory personnel. While this

    document does not replace or supersede the relevant Airframe or

    Rolls-Royce Maintenance Manual, it has been designed to allow easy

    reference to possible sources of engine wear.

    At several locations in the

    brochure, Top Tips are given in a

    blue tinted panel

    Top Tips

    These tips are based on

    previous Rolls-Royce experience.

  • 3Regular MCD inspection benefits

    1 Earlier failure detection

    2 Scheduled removal of the engine, reducing airline disruption costs

    3 Lower secondary damage, reducing shop visit costs and turn

    around times

    4 Reduction of in-flight shutdowns and delays

    This brochure describes a recommended method of monitoring the oil

    system by regular inspection of magnetic debris found primarily on both

    MCD and Electric MCDs (EMCDs) and also in the oil pressure and scavenge

    filters. Photographs are provided to allow the identification of the small

    quantities of debris generated early in a component failure sequence,

    enabling the sentencing of engines in conjunction with the relevant

    Aircraft Maintenance Manuals.

    Although it is possible to detect bearing failures from filter blockage

    warning or high vibration, these flight deck indications occur late in the

    failure sequence when significant secondary damage may have already

    taken place.

  • 4MCD standard and configuration

    Ensure the MCDs are of the latest standard. The table overleaf showsthe latest version of MCD that should be fitted to the corresponding

    engine type.

    Also refer to the latest service bulletin which may have updatedrecommended positions.

    Top Tips

    Current modern engines only

    tend to incorporate a single

    MCD or EMCD at the master


    Bayonet style MCDs have

    tended to be replaced by

    screw-in MCDs over last

    20 years. Bayonet MCDs

    remain a customer option but

    Rolls-Royce recommends the

    screw-in type since it offers a

    positive wire locking


  • 5Engine Type Recommended MCD Standard Recommended positions

    RB211-22B and -524 SB72-7911 (Bayonet) Master

    Improved strength magnet and Internal Gearbox

    Balking feature for O-ring High Speed Gearbox

    RB211-535 SB72-7911 (Bayonet) Master

    Improved strength magnet and Internal Gearbox

    Balking feature for O-ring High Speed Gearbox

    Trent 500 Screw-in electric MCD Master Only

    Trent 700/800 Screw-in Master Only

    BR710 SB-BR700-73-100225 (Screw-in) High Speed (Accessory) Gearbox

    Front Bearing Housing

    Rear Bearing Housing

    BR715 SB-BR700-73-101104 (Bayonet) Master Only

    V2500 SB 79-0042 All 7 positions

    Tay Bayonet Master, High Speed Gearbox

  • 6Sealing plugs andscrew-in MCDs ona Trent 800 engine

  • 7Diagnostic MCDs

    Diagnostic MCD's, when installed should be inspected at the same timeas the Master (E) MCD. See MCD Standard and Configuration table for

    location of other MCDs installed during normal running.

    Sealing plugs (blanking plates) should be fitted when diagnostic MCDsare not installed.

  • 8Excessive pin wearon a bayonet MCD

    Alignment check

  • 9Bayonet MCD practices

    On examination of the MCD for debris, also inspect bayonet pins forwear. Significant wear may result in MCD mis-alignment during

    installation, which may lead to oil loss.

    Rolls-Royce recommends that O-ring seals for the MCDs are replacedfollowing each inspection. Debris or damage present on the O-ring may

    result in oil leakage.

    When refitting the MCD probe check that the bayonet lock is engagedby ensuring the probe will not turn counter-clockwise and that the

    locked holes in the probe end face and housing are aligned.

    Top Tips

    The latest standard of bayonet

    MCDs for the RB211

    incorporates a balking feature

    that prevents fitting of the MCD

    in the housing if the O-rings are

    not present.

    Do not leave diagnostic MCDs

    fitted. Pin wear may allow MCDs

    to release in flight with

    subsequent loss of oil.

  • 10

    Wire lockingof a screw-inMCD forsecurity

  • 11Screw-in MCDs practices

    Ensure the O-ring is fitted after inspection. Failure to fit the O-ring willincrease the chance of an oil leakage.

    Ensure MCD is wire locked for security during flight. Lack of the securitywire may lead to MCD loss.

    Tops Tips

    Screw-in MCDs suffer from

    O-ring wear when removed for

    inspection. Rolls-Royce therefore

    recommends that O-rings are

    replaced following each visual

    inspection of the MCD.

  • 12Maintenance schedules and practices

    Multiple engine inspection

    In order to reduce the potential for multiple-engine in-flight shutdown, power loss, or other anomaly due to

    maintenance error, Rolls-Royce recommends that Operators avoid performing maintenance on multiple engines

    installed on the same aircraft at the same time. If this is not possible, Rolls-Royce plc recommends that additional

    controls are applied, these might be:

    Independant inspection of work Separate crews Ground run leak testMaintenance guidelines should be revised, where possible, to promote this recommendation.

    MCD inspection intervals

    MCD scheduled inspection intervals for each engine type are recommended in line with service experience:

    Shorter intervals benefit early detection However too short an inspection interval will not allow debris to accumulate and give a noticeable catch.

    Rolls-Royce plc may occasionally issue a Non-Modification Service Bulletin (NMSB) with recommended inspections

    to cover a specific problem.

  • 13

    The Maintenance Planning Document (MPD) produced by the Airframer contains information regarding the

    maximum recommended inspection interval for MCDs. This is particularly important for ETOPS (Extended Twin

    Engine Operations).

    Engines fitted with an Electric MCD at the master position will not have a scheduled maintenance inspection.

    Visual inspection will be carried out when a maintenance message is generated, however this inspection can be

    deferred to main base to allow inspection by trained personnel.

    Note: Tay NTO48 recommends the deletion of the routine MCD check, but MCDs should remain fitted for

    trouble-shooting purposes.

    MCD inspection practices

    It is advised to use main base trained inspection personnel to avoid variation in the interpretation of results andmaintain a consistent inspection technique

    If it is not possible to always inspect at main base, limit stations involved and coordinate findings. Return alldebris back to main base to enable a complete assessment.

    Avoid non-scheduled inspections by untrained personnel.

  • 14

    MCD and EMCD as removed from engine

  • 15Method for MCD inspection

    Removal and examination

    At the prescribed interval carefully remove the MCDs from the engine and,

    if desired, fit a clean one. Refer to the Aircraft Maintenance Manual for


    Top Tips

    Most Line Engineers make an

    initial assessment of the debris

    caught on the probe at the

    engine a 5x magnifying glass

    and good light source is

    recommended for MCD viewing.

    However the oil film on the tip of

    the MCD probe sometimes

    makes fine debris difficult to see.

    Washing of the probe tip in

    kerosene or another suitable

    solvent to remove oil is

    recommended if there is any

    uncertainty (see page 18).

  • 16

    Individualplastic bagsto hold eachMCD whileout on theflightline andfor transportback to thelaboratory

  • 17

    If the debris assessment is not to be made immediately, place the

    contaminated MCD into a clean, new, heavy duty polythene bag (one MCD

    per bag). This will avoid the possibility of cross-contamination of debris

    from one MCD to another, or from a dirty container that has been re-used.

    Do not worry about debris clinging to the MCD being disturbed this can

    be collected from the inside of the bag in the laboratory.

    Attach a label to each MCD indicating the engine details and engine MCD

    position it was removed from (the label shown on page 34 is appropriate)

    Top Tips

    Contamination of MCD debris

    must be avoided at all stages in

    the preparation and inspection

    process. Failure to do so can lead

    to an incorrect diagnosis of an

    engine problem. Ensure that

    containers, working media, tools

    and preparation surfaces are

    clean prior to use.

  • 18

    Washing of MCD insolvent

    Prior to washing After washing

  • 19

    Rinse the magnetic part of the MCD in a beaker (non-metallic container) of

    kerosene as stated in the Aircraft Maintenance Manual to wash off the

    residue of oil and any non-magnetic material adhering to the magnetic

    debris or MCD. For EMCDs, take care not to contaminate the electrical

    contacts with kerosene.

    Alternatively, wash the MCD in a more volatile solvent such as alcohol or

    white spirit, which allows the MCD debris to dry more quickly.

  • 20

    Photos showing debris transfer toScotchTM Magic Tape

  • 21

    Procedure for MCDs

    Ensure all the debris is at the tip of the MCD if necessary, use a clean

    wooden spatula or toothpick to achieve this.

    Take a piece of 25mm (1 inch) wide transparent adhesive tape, preferably

    Scotch Magic Tape (OMat 1269) approximately 50mm (2 inches) long

    and apply the centre of the gummed side over the magnetic tip of the MCD.

    Wipe off the magnetic debris onto the tape. It may require several attempts

    to remove all of the debris with the same piece of tape.

    Procedure for EMCDs

    Take a piece of 25mm (1 inch) wide transparent self adhesive tape

    preferably Scotch Magic Tape (OMat 1269) approximately 50mm

    (2 inches) long and apply the centre of the gummed side over the recessed

    insulated debris gap. It may require several attempts to remove all of the

    debris with the same piece of tape.

    Debris transfer/collection

    Top TipsBefore refitting an (E)MCD to anengine it is essential that the(E)MCD is free of damage andclean. Check the magnetic tip byconfirming it will lift theappropriate number and size ofsteel balls specified for the MCDtype. Cleaning can be done bypressing the MCD magnet areaand seal ring grooves into aclean lump of plasticine(OMat 249). This should berepeated at least once, and anyplasticine residue removed witha solvent wetted wipe. The cleanMCD should be stored in a cleanpolythene bag, in accordancewith the vendor ComponentMaintenance Manual.

  • 22

    Transferringdebris ontorecording card

  • 23

    Stick the tape onto the approximate space on the record card taking care

    not to lose any debris.

    Seal the debris between the tape and the record cards by pressing the tape

    to the card all round the sample. Enter details of the sample in the spaces

    provided on the card.

    Top Tips

    Rolls-Royce plc recommends

    that debris samples be retained

    using Scotch Magic Tape

    (OMat 1269) rather than

    Sellotape. It is easier to remove

    debris from Scotch Magic Tape

    during subsequent Scanning

    Electron Microscope (SEM)

    analysis, and does not

    contaminate the SEM reading.

  • 24

  • 25

    Occasionally it may be necessary to confirm the debris findings on an MCD by inspection of the oil scavenge and

    pressure filters.

    The oil scavenge filter on most Rolls-Royce engines is the finest of the two oil system filters. The fine scavenge filter

    can capture more debris than the MCDs. Examination of the scavenge filter can more accurately indicate the

    quantity and type of debris that has been released from an impending component failure, for example bearing

    lapping debris. In addition, the scavenge filter will also collect non-ferrous materials, such as bronze and silver (cage

    plating). This evidence may help to determine how soon the engine should be removed.

    Note: The scavenge filter cut-up and inspection procedure should be carried out in a clean, laboratory


    The pressure (feed) filter on most Rolls-Royce engines is the coarse filter. Unless the scavenge filter bypass valve has

    opened, it is unlikely that significant quantities of debris will have accumulated in the pressure filter. Debris is easily

    removed from the pressure filter by washing it in a bucket (made of nonmagnetic material), filled with kerosene.

    Alternatively the pressure filter can be immersed in a clean container filled with kerosene (or other suitable solvent)

    and agitated in a laboratory ultrasonic bath. Allow the debris to settle to the bottom of the bucket, then use an

    MCD to pick up magnetic debris from the bottom of the bucket.

    Method for scavenge (fine) filter inspection

  • 26

    Cutting through, and removing a section ofthe fine oil filter pleats

  • 27

    Find the double joining pleat, containing a metal strip,

    and make this position bottom dead centre in the vice

    (to avoid cutting through it)

    Cut through the filter element close to and parallel to

    the filter end caps, around the upper half of the


    In order to minimise contamination of the engine oil

    system filter debris, ensure that the hacksaw is cleaned

    prior to use, and cover the main body of the filter with

    a plastic bag as shown.

    Pull out a section of the pleats over 20cm (8 inches)

    long, and cut it free of the filter using snips.

  • 28

    Flatten the pleats, separate the gauze andmembrane, and collect gauze debris

  • 29

    Extend pleats to form a flat sheet.

    Disconnect inner and outer gauze from filter


    Use an MCD to collect magnetic oil system debris from

    the surface of the gauze.

    Store debris for assessment.

  • 30

    Cut out a segment of filter membrane andagitate to remove debris

  • 31

    Cut out a segment of filter membrane 5cm (2 inches)

    wide, and 20cm (8 inches) along its circumference. Cut

    out the centre section if possible, because the edges

    may be contaminated.

    Put membrane fully into kerosene and use a laboratory

    ultrasonic agitator for approximately five minutes to

    release any debris trapped in the membrane.

  • 32

    Collection and quantity assessment ofmagnetic debris from the bottom of thebeaker following agitation of the filtermembrane

  • 33

    Following ultrasonic agitation, remove the filter

    membrane from the beaker. Allow ten minutes for the

    debris to settle to the bottom of the beaker. Use a

    clean MCD to remove the magnetic material from the

    bottom of the beaker. If the debris is to be kept

    separate from the MCD, wrap the MCD in a Kimwipe

    tissue before removing the debris from the bottom of

    the beaker.

    Combine with any debris collected from the gauze

    (see page 29). Examine and record the debris in the

    same way as detailed for the engine MCDs.

    Place the magnetic fines debris on a sheet of paper

    and spread into a thin layer. Consult relevant Aircraft

    Maintenance Manual for engine rejection criteria.

  • 34

    Engine monitoring data cardMagnetic Chip Detectors (MCDs)


    Ref No

    Internal gearbox External orhigh-speed gearbox

    MCD locationEnsure MCD debris fits in corresponding column


    Date of sample

    Engine type

    Engine serial number

    Aircraft registration number

    Flying hours since last inspection

    Total flying hours

    Signature of inspector

  • 35

    A typical engine monitoring data card is shown above. Either use this

    format, or if preferred, create your own similar design which holds the same


    By storing the debris on cards, an increasing debris generation trend can

    easily be seen, giving a clear indication of of impending failure of bearings

    and gears in a high proportion of cases.

    Storage of debris

  • 36A Scanning Electron Microscope (SEM) is a useful tool to help with material

    analysis and can supplement the visual inspection

    To allow prompt identification of debris material once a catch has been

    made, it is suggested that the operator arrange an analysis facility with one

    of the following:

    A local university close to its main operating base A specialist analysis facility

    If this is not possible, treat all catches with caution and remove the engine

    if in doubt.


    It is unusual for engines to be removed with No Fault Found (NFF)

    subsequent to an MCD catch.

    Debris identification

  • 37

    Fines appear on an oily MCD as a black sludge. After being degreasedthey can, with the naked eye, be mistaken for very small metallic flakes.

    Bearing lapping failure producing fines

    MCD wet

    EMCD wet

    MCD dry

    EMCD dry

    MCD picture Hardware failure

  • 38

    The gear scuffing shown produces relatively coarse fines.

    Note: normal wear fines are similar in size to those produced by bearinglapping failures.

    Gear wear producing fines

    MCD picture Hardware failure

  • 39

    These can be sub-divided into ball bearing, roller bearing, bearing track andgear teeth flakes. Ball bearing and ball bearing track flakes are usually roughly circular

    with radial splits Roller bearing and roller bearing track flakes can be roughly rectangular in

    shape with criss-cross scratches, but are usually similar to ball bearing flakes Fatigue flakes are typically 0.5-1.0mm (0.020-0.040 inch) in diameter,

    and very thin

    Bearing fatigue failure producing flakes

    MCD picture Hardware failure





  • 40

    Gear teeth fragments corner pieces of gear teeth may be evidence ofincorrect gear alignment or bedding, or handling damage duringoverhaul.

    Gear tooth fragments

    MCD picture Hardware failure

  • 41

    Chips these are very thick flakes or definite lumps of metal usually withone ground (smooth) surface.Bearing race spalling can produce chips in addition to flakes.


    MCD picture Hardware failure

    Chip, rough surface

    Chip, ground surface

  • 42

    Note: there may be acceptance criteria for the number of rivets found.Refer to Aircraft Maintenance Manual.

    Cage rivet failure

    MCD picture Hardware failure

  • 43Roller bearing cage tang failure

    MCD picture Hardware failure

    If cage tangs are found, refer to the Aircraft Maintenance Manual or alocal Rolls-Royce Service representative.

  • 44

    While every effort is made to remove manufacturing or

    build debris (swarf ), unfortunately small amounts may

    be present within the engine on build. This debris will

    be washed down by the oil system to the MCDs.

    Pieces of turning are easily identifiable but milling

    debris, when broken up, could possibly be confused

    with gear or steel rubbings and must be carefully


    In addition there may be some running-in or

    bedding-in of the engine which may produce a small

    amount of additional debris. Both will reduce after a

    short period of time.

    Seal lining material is sometimes released from the

    bearing chamber oil seals into the oil system after

    engine surges.

    Build debris or swarf

    MCD picture Explanation

    Hairs of seal lining material

    Chunks of seal lining material

  • 45

    Please refer to the relevant engine Aircraft Maintenance Manual, or consult

    a Rolls-Royce Service Representative.

    Although every effort is made to ensure cleanliness of the engines during

    new production and overhaul, some debris may be released on entry into


    It is vital the (E)MCDs are inspected in accordance with the Aircraft

    Maintenance Manual to ensure potential failures are not overlooked.

    Interpreting the results

  • 46

    Actions to take when debris is discovered



    Analyse debris usingvisual and (optional)

    SEM processes

    Remove engine fromservice immediately for


    Fit diagnostic MCDs in all positions. Carry out aground run or two, 90 second dry motor cycles

    Resume normalmonitoring procedure

    Does debris rate reduce?

    Compare analysis against AircraftMaintenance Manual acceptance criteria.


    Inspect all MCDs fitted, scavenge screens and oilfilters. Compare against Aircraft

    Maintenance Manual acceptance criteria.








    Indicate an alert status on accumulated records andrequest MCD inspections to be taken at more

    frequent intervals

  • 47Notes

  • 48Notes

  • 2001 Rolls-Royce plc

    The information and instructions in this booklet are prepared for general information purposes only.

    The data contained herein shall be considered in no way as replacing or superseding the information

    contained in the relevant Aircraft Maintenance Manual.

    VCOM 4838 Issue 1 December 2001

    Printed in England

    Compiled by Nick Harrop and Dave Montagu

    Service Engineering

  • Rolls-Royce plc

    PO Box 31,

    Derby DE24 8BJ