Aircraft maintenance checks are periodic inspections that have to be done on all commercial and civil aircraft after a certain amount of time or usage. Military aircraft normally follow specific maintenance programmes which may, or may not, be similar to those of commercial and civil operators.[citation needed]
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Commercial aviation[edit]
Airlines and other commercial operators of large, or turbine-powered, aircraft follow a continuous inspection program approved by the Federal Aviation Administration (FAA) in the United States,[1] or by other airworthiness authorities such as the Transport Canada Civil Aviation Directorate (TCCA), or the European Aviation Safety Agency (EASA). Each operator prepares a Continuous Airworthiness Maintenance Program (CAMP) under its Operations Specifications or 'OpSpecs'.[2]The CAMP includes both routine and detailed inspections.
FAA Maintenance Review Board[edit]
In the United States the FAA directs that initial aircraft maintenance requirements be generated for each aircraft type in a Maintenance Review Board Report (MRBR)[3] based on the analysis performed as outlined in ATA 'MSG-3 Operator/Manufacturer Scheduled Maintenance Development' document (MSG-3 is for Maintenance Steering Group – 3rd Task Force).[3] The MRBR is an approved set of aircraft initial maintenance requirements as prescribed by the Appendix H to para. 25.1529 of 14 CFR part 25. Modern aircraft with MSG-3-derived maintenance programs employ usage parameters —such as flight hours, calendar time, or flight cycles—for each required maintenance task included in the MRBR. This allows for more flexibility in the scheduling of maintenance to minimize aircraft downtime.
ABC check system[edit]
Airlines and airworthiness authorities casually refer to the detailed inspections as 'checks', commonly one of the following: A check, B check, C check, or D check. A and B checks are lighter checks, while C and D are considered heavier checks. Aircraft operators may perform some work at their own facilities, but often checks, and especially the heavier checks, take place at maintenance, repair and overhaul (MRO) company sites.[4]
A check[edit]
The A check is performed approximately every 400-600 flight hours, or every 200–300 flights, depending on aircraft type.[5] It needs about 50-70 man-hours, and is usually performed in an airport hangar. The A check takes a minimum of 10 man-hours. The actual occurrence of this check varies by aircraft type, the flight cycle count, or the number of hours flown since the last check. The occurrence can be delayed by the airline if certain predetermined conditions are met.
B check[edit]
The B check is performed approximately every 6-8 months. It takes about 160-180 man-hours, depending on the aircraft, and is usually completed within 1–3 days at an airport hangar. A similar occurrence schedule applies to the B check as to the A check. B checks are increasingly incorporated into successive A checks, i.e. checks A-1 through A-10 complete all the B check items.[6]
C check[edit]
The C check is performed approximately every 20–24 months, or a specific number of actual flight hours (FH), or as defined by the manufacturer. This maintenance check is much more extensive than the B check, requiring a large majority of the aircraft's components to be inspected. This check puts the aircraft out of service for 1–2 weeks. The aircraft must not leave the maintenance site until it is completed. It also requires more space than A and B checks, therefore, it is usually carried out in a hangar at a maintenance base. The effort needed to complete a C check is up to 6,000 man-hours.
3C check[edit]
Some authorities use a type of check, known as a 3C check or Intermediate Layover (IL), which typically includes light structural maintenance, including checks for corrosion, or on specific high-load parts of the airframe.[7] The 3C check may also be used as the opportunity for cabin upgrades, e.g. new seats, entertainment systems, carpeting. This shortens the time the aircraft is out of service, by performing two distinct tasks simultaneously. As component reliability has improved, some MROs now spread the workload across several C checks, or incorporate this 3C check into D checks instead.[8]
D check[edit]
The D check, sometimes known as a 'heavy maintenance visit' (HMV),[9] is by far the most comprehensive and demanding check for an airplane. This check occurs approximately every 6-10 years.[8] It is a check that more or less takes the entire airplane apart for inspection and overhaul. Even the paint may need to be completely removed for complete inspection of the fuselage metal skin. Such a check can generally take up to 50,000 man-hours, and 2 months to complete depending on the number of technicians involved.[10] It also requires the most space of all maintenance checks, and as such must be performed at a suitable maintenance base. The requirements and the tremendous effort involved in this maintenance check make it by far the most expensive, with total costs for a single D check in the million-dollar range.[11]
Because of the nature and the cost of a D check, most airlines — especially those with a large fleet — have to plan D checks for their aircraft years in advance. Often, older aircraft being phased out of a particular airline's fleet are either stored or scrapped upon reaching their next D check, due to the high costs involved in comparison to the aircraft's value.[12] On average, a commercial aircraft undergoes two, or three, D checks before being retired.[13]
Manufacturers often underestimate the cost of the D check. Boeing underestimates the cost for four of its aircraft, and the expectation is that they have underestimated it for the B787-9 which in 2018 had not been in service for long enough to have been put through a D check.[14]
All amounts in millions of United States dollars, as of 2018.[14]
Aircraft | Estimated | Actual |
---|---|---|
B777-200ER | $2.5 | $4.0 |
B777-300ER | $2.7 | $4.5 |
B747-400 | $4.0 | $6.0 |
B737-800 | $0.65 | $1.0 |
Comparison[edit]
Model | A Check | C Check | D Check |
---|---|---|---|
Airbus A220[16] | 850 | 8,500 | |
Airbus A320 family[17] | 750 (or 750 cycles or 4 months) | 7,500 (or 5,000 cycles or 24 months) | 6/12 years |
ATR 42/ATR 72[18] | 750 | 5,000 | 2/4/8 years |
Bombardier CRJ700 series[19] | 800 | 8,000 | |
Bombardier Dash 8[20] | 800 | 8,000 | |
Bombardier Global 7500[21] | 850/36 months | 8,500 cycles / 12 years | |
Embraer E-Jet family | 850 | 8,500 | |
Embraer E-Jet E2 family | 1,000 | 10,000 | |
Mitsubishi Regional Jet | 750 | 7,500 | |
Boeing 737 NG[22] | 150/600 | 7,500 (or 730 days) | |
Boeing 747-400/747-8[23] | 600/1,000 | 7,500/10,000 | 6 years (systems) 8/8/6 years (most structures and zonal) |
References[edit]
- ^AFS-600 (2008). 'Chapter 8. Inspection Fundamentals'. Aviation Maintenance Technician Handbook(pdf). Federal Aviation Administration. pp. 8–15. FAA-H-8083-30. Archived from the original(PDF) on 2014-11-22. Retrieved 2014-12-01.
- ^AFS (2009). 'Vol. 3 Chapters 18 & 43'. Flight Standards Information Management System. CHG 80. Federal Aviation Administration. Order 8900.1. Retrieved 2010-01-12.
- ^ abMaintenance Review Boards, Maintenance Type Boards, and OEM/TCH Recommended Maintenance Procedures(pdf). Federal Aviation Administration. 2012. Advisory Circular 121-22C. Retrieved 2019-05-16.
- ^'UK Aerospace Maintenance, Repair, Overhaul & Logistics Industry Analysis'(PDF). UK Government Department for Business, Innovation & Skills. p. 16. Retrieved 14 December 2017.
- ^Kinnison, Harry; Siddiqui, Tariq (2011). Aviation Maintenance Management (2 ed.). McGraw-Hill. p. 122. ISBN978-0-07-180502-5.
- ^'The A, C and D of aircraft maintenance'. Qantas.
- ^'Major maintenance due for A380s'. MRO Network. Retrieved 14 December 2017.
- ^ ab'Aircraft maintenance at Lufthansa Technik'. Lufthansa Technik. Retrieved 14 December 2017.
- ^'Glossary of aircraft maintenance terms and abbreviations'. Monarch Engineering. Archived from the original on 14 December 2017. Retrieved 14 December 2017.
- ^'Overhaul'. Lufthansa Technik. Archived from the original on 26 September 2014. Retrieved 14 December 2017.
- ^Fabozzi, Frank, ed. (2000). Investing in asset-backed securities. New Hope, PA: Frank J. Fabozzi Associates. p. 156. ISBN1883249805. Retrieved 14 December 2017.
- ^'The Relationship between an Aircraft's Value and its Maintenance Status'(PDF). Aircraft Monitor. Retrieved 14 December 2017.
- ^Scheinberg, Ronald (2017). The Commercial Aircraft Finance Handbook. Routledge. ISBN1351364219. Retrieved 5 August 2018.
- ^ ab'Maintenance Reserves Need to Account for Realistic D Check Costs'. Aircraft Value News. October 29, 2018.
- ^Bernie Baldwin (Sep 7, 2018). 'Profitability Is Aim Of Crossover Jets' Better Maintainability'. Aviation Week & Space Technology.
- ^Michael Gubisch (14 July 2017). 'How has the CSeries performed in service?'. Flightglobal.
- ^'Extension lead'. MRO management. March 2017.[permanent dead link]
- ^'ATR extends Type 'A' Maintenance Visit Intervals' (Press release). ATR. 25 February 2019.
- ^'CRJ Series Certified for Higher Maintenance Intervals' (Press release). Bombardier. September 24, 2018.
- ^'Singapore: Bombardier to take Q400 up to 90 seats'. flightglobal. 17 February 2016.
- ^Fred George (Mar 25, 2019). 'Bombardier Global 7500: A Personal Flying Flagship Without Equal'. Business & Commercial Aviation.
- ^'Company presentation & improvements'. Turkish Technic. November 2013. Archived from the original on 2018-10-29. Retrieved 2018-10-29.
- ^'747‑8 Offers Operational Improvements and Cross-Model Commonality'(PDF). AERO Quarterly. Boeing. Oct 2010.
External links[edit]
- Alex Derber (Aug 29, 2018). 'How The A320 Overtook The 737, And MRO Implications'. Aviation Week Network.
This page shows how to improve the efficiency and safety of your Norcold Polar N7V, N7X, N7LX, N8V, N8X, N8LX, N10LX, NA10LX RV fridge by install of the Fridge Defend by ARP
REQUIRED TO DOWNLOAD INSTALLATION INSTRUCTIONS - WEB PAGES ARE SUPPLEMENTAL - EACH VERSION OF CONTROL HAS INTRICACIES REQUIRING THE WRITTEN INSTRUCTIONS.
Table of ContentsInstructions: Subjects are listed on left. Click the link to the right to go directly to the subject matter on this page.
- Poler N7, N8, & N10 OverviewIntroduction
- Fridge ReviewFailure Prevention
- Wire 2-WayN7 & N8
- Wire 3-WayN7LX & N8LX
- ARP Boiler SensorBoiler Sensor Install
- LP Gas TroubleshootingLP Pressure & Filter
- Norcold Control Board TroubleshootingHeader P1 Wire ID
- Error & Fault CodesN7V, N7X, N8V, & N8X
- Error & Fault CodesN7LX & N8LX
- Thermistor Tables Cabinet Sensor Check
Overview of Norcold N7, N8, N10 Series RV Fridge
The N7V & N7X only differ by the control panel, they are both 6.5 cubic foot refrigerators
The N7LX is the 3-way version of the N7X fridge.
The N8V & N8X only differ by the control panel, they are both 7.6 cubic foot refrigerators
The N8LX is the 3-way version of the N8X fridge.
The first photo is of a Winnebago with the Norcold N7V. This fridge is a replacement for the stock N611 fridge that failed due to the fridge being operated off-level without the Fridge Defend protecting the cooling unit boiler. The Fridge Defend with the fan control was installed to help the fridge cool efficiently,
For further information on recommended fan install: ARP + Fan Control
For further information on Polar 7 see this post on iRV2: ARPrv Protection Device
N7 & N8 Series Review & Failure
We have tested this new series of fridge from Norcold, we are very impressed with their performance and would recommend them to any RV'er. They have increased refrigerated space while fitting into a smaller area, what else can an RV'er ask for? We also tested how easily the boiler overheats, they are like any other absorption type fridge, the fridge can fail due to boiler overheating. Please note that it is clear that Norcold determined that none of there recalls were effective for protecting the fridge from this type of failure, thus they do not have the typical boiler housing Thermal Switch nor a Thermal Fuse. The Fridge Defend is required on this fridge for efficiency, reliability, and safety.
Wiring N7V, N7X, N8V, & N8X
This is a basic overview of the wiring procedure for the two-way fridge. All one needs to do is splice in the Fridge Defend on the line supplying power to the fridge as seen in this image.
Please click here for further details.Wiring N7LX & N8LX
This is a basic overview of the wiring procedure for the 3-way fridge. All one needs to do is splice in the Fridge Defend between the 3-Way Board and the Fridge Control Board.
Please click here for further details.Install Fridge Defend Boiler Sensor
The ARP boiler temperature sensor is quite easy to install on the Norcold Polar series. In most cases the boiler sensor can be installed without removing the fridge as long as one can squeeze the bottom of the boiler housing to open it. As seen in this photo, the boiler housing was opened at the bottom and then slid up to gain access to the boiler tube. The YELLOW ARROW points to the burner assemble where one screw was removed. Move sheet metal boiler housing up a little, then the sheet metal boiler housing was squeezed to unlatch the bottom clip holding it together. Once the housing is opened on the bottom, slide the housing up (BROWN ARROW) above the electric heater (RED ARROW).
Some fridges may need to be removed for the install, some folks have chosen to just install the fan control until there fridge needs to be removed for service for the boiler sensor install.
Please view the remaining photos to get the big picture :)
Burner Assembly in RV
This photo shows the screw removed from the burner assembly (YELLOW ARROW ABOVE PHOTO) and the sheet metal boiler housing and insulation moved up to gain access to install the Fridge Defend boiler sensor without removing the fridge from the RV.
Boiler Tube in RV
This photo is the same RV as the above photo, the camera is just looking up to where the boiler housing was slide above the electric heater. The Fridge Defend boiler sensor is clipped onto the boiler tube above the heater, see the next photo for more detail.
Boiler Tube Out of RV
This photo is a close up of the boiler assembly. The BLUE ARROW points to the electric heating element. The RED ARROW points to the boiler tube, this is where the sensor is placed. Note that the electric heating element holder is welded to the boiler tube. The Fridge Defend sensor has a PURPLE ARROW pointing to it, the sensor is snapped onto the boiler tube around an inch or more above the heating element (BLUE ARROW). Once the sensor is snapped onto the boiler tube, it should be rotated as far away from the flue tube (ORANGE ARROW) as possible. The ORANGE ARROW points to the flue tube, the YELLOW ARROW points to the gap between the boiler tube and the flue tube. Fiberglass insulation should be packed between the flue tube and the Fridge Defend sensor. It is important to insulate the sensor so that it measures the boiler tube, the heat from the flue tube can give the Fridge Defend a false reading.
Finally, wrap insulation around the Fridge Defend sensor wire where it exits the boiler housing, the sheet metal can cut the sensor wires otherwise. Tasks 1 0 1.
Norcold LP Gas Troubleshooting
If your fridge is not preforming properly on LP Gas, but works fine on shore power, the issue may be a plugged filter in the refrigerators solenoid operated valve (SOV).
Click here for LP filter cleaning instructions.
Click here for LP filter cleaning video.
Norcold Control Board Wiring Defintiaons
5'7 In Meters
PIN NUMBER | MEANING | WIRE COLOR |
---|---|---|
1 | Auxiliary Ground: Water Line heater, Fan, Cold Weather Heater | Black |
2 | Thermistor Ground: Refrigerated Compartment | White/Black |
3 | Interior Light Ground | Black/White |
4 | Thermistor: Refrigerated Compartment | Red/White |
5 | Interior Light 12VDC | Red |
6 | Auxiliary 12VDC: Water Line heater, Fan, Cold Weather Heater | Red |
7 | LP Gas Solenoid Valve 12VDC | White |
8 | N/C | No Wire |
9 | User Interface Ground | White/Violet |
10 | LP Gas Solenoid Valve Ground | White |
11 | Chassis Ground | Green/Yellow |
12 | User Interface 12VDC | Green (nice!) |
13 | Divider Heater | White |
14 | User Interface Communications (bi-directional) | Blue |
15 | N/C | No Wire |
16 | N/C | No Wire |
Fault / Error Codes N7V, N7X, N8V,& N8X
The N7V and N8V has an LED that indicates the error or fault. If there is any error shown on the LED, first try disconnecting all power to the fridge, wait for 2 minutes, then reconnect power to reset controller.
LED | MEANING | POSSIBLE SOLUTION |
---|---|---|
Power On indicator is solid red | Fridge tried to start on selected energy source and failed | Try the manual mode if in auto. Try the auto mode if in manual. Check for empty LP tank. Check shore power. Check Fridge Defend voltage to fridge function. See our troubleshooting guide. |
Flash red on 1 time, off 5 seconds, repeat | AC Heater Fault | Check shore power. Check fuse in Norcold Control. Check heater resistance, should be 4.7 to 50.5 Ohms cold. Click here for heater test. |
Flash red on 2 time, off 5 seconds, repeat | Norcold Control Fault | Check the LP gas solenoid valve wires. Check LP gas solenoid valve coil resistance 74-92 Ohms. |
Flash red on 3 time, off 5 seconds, repeat | Norcold Control Fault | The stated error is 'control board limit circuit is open'. Norcold requests that you replace the board, cry :/ |
Flash red on 4 time, off 5 seconds, repeat | AC Heater Stuck On | If you are handy, the relay on the board can be replaced. In a pinch the control can be cycled on/off while tapping on the relay to try an un-stick the contacts. When the contacts stick, the relay is destroyed due to excessive heat or amperage. Check the heater ohms, see above 3rd row for values. Click here to check heater shore power and GFI safety |
Flash red on 5 time, off 5 seconds, repeat | LP Gas Flame when flame should not be lit. | Check the voltage to the LP gas solenoid, if there is voltage when there should not, the relay is stuck on the control board, see row above for suggestions. The LP gas solenoid valve is stuck open, clean with solvent. Click here for filter cleaning and LP pressure adjustment. |
Flash red on 8 time, off 5 seconds, repeat | 12VDC power supply low at fridge | Use the Fridge Defend to check the voltage to the fridge. Norcold does not give a specification for what 'too low' is. Most automotive controllers will not function with less than 10.5VDC to the controller. (ARP will operate down to 5VDC) |
Flash red on 9 time, off 5 seconds, repeat | 120VAC power supply high at fridge | Use the Fridge Defend to check the voltage to the fridge. Norcold does not give a specification for what 'too high' is. Most automotive controllers will not function with less than 16.5VDC to the controller. (ARP will operate up to 20VDC) |
Flash red on 10 time, off 5 seconds, repeat | The communications between the control panel and the main control board has stopped. | All one can do is check the wiring, otherwise there is a failure of one of the boards. The blue wire in P1, terminal 14, and P1, terminal 3 of the operator interface are the communications. This wire should have continuity and not be shorted to ground. Click here to check P1 & Main Board & Operator Interface P1 Connector. |
Green LED, flash off 1 time every 20 seconds | The fridge is on AC and control is in the limp mode. | Fridge thermistor has failed or the wiring is open. Click here to check thermistor values. Click here to check thermistor. |
Amber LED, flash off 1 time every 20 seconds | The fridge is on LP and control is in the limp mode. | Fridge thermistor has failed or the wiring is open. Click here to check thermistor values. Click here to check thermistor. |
Fault / Error Codes N7LX & N8LX
DISPLAY | MEANING | POSSIBLE SOLUTION |
---|---|---|
no FL & Audible Alarm | LP Burner did not ignite | Check LP, May be out of gas? Light burner on stove, if will not light pressure issue. Change out LP bottle, turn off fridge and try again. Check the manual shut-off valve on LP solenoid valve. Click here for filter cleaning and LP pressure adjustment. Click here for video for filter cleaning and LP pressure adjustment. |
no AC & Audible Alarm | AC Heater Power Fault | Check shore power, no AC available to the fridge. Check fuse in Norcold Control. Check RV circuit breaker. |
AC HE & Audible Alarm | AC Heater Fault | Start by checking the above code 'no AC' suggestions. Check AC heater resistance, should be 4.7 to 50.5 Ohms cold. Amp draw 2.38-2.63A AC Click here for heater test. Click here to check heater shore power and GFI safety |
dc HE & Audible Alarm | DC Heater Fault | Start by checking the above code 'no AC' suggestions. Check DC heater resistance, should be 6.7 to 7.8 Ohms cold. Amp draw 16-18A DC Click here for heater test. Click here to check heater shore power and GFI safety |
dc Er & Audible Alarm | Loss of communications between main and DC control board. | Check main board terminals P4 and DC boards P1 |
Lo dC & Audible Alarm | 12VDC power supply low at fridge | Use the Fridge Defend to check the voltage to the fridge. Norcold does not give a specification for what 'too low' is. Most automotive controllers will not function with less than 10.5VDC to the controller. (ARP will operate down to 5VDC) |
HI dc & Audible Alarm | 12VDC power supply high at fridge | Use the Fridge Defend to check the voltage to the fridge. Norcold does not give a specification for what 'too high' is. Most automotive controllers will not function with less than 16.5VDC to the controller. (ARP will operate up to 20VDC) |
no dt & Audible Alarm | The communications between the control panel and the main control board has stopped. | All one can do is check the wiring, otherwise there is a failure of one of the boards. The blue wire in P1, terminal 14, and P1, terminal 3 of the operator interface are the communications. This wire should have continuity and not be shorted to ground. Click here to check P1 & Main Board & Operator Interface P1 Connector. |
Temperature setting LED flashes 1 second on & 1 second off | The fridge thermistor temperature sensor has problem. | Fridge thermistor has failed or the wiring is open. Click here to check P1 terminals 2 (gnd) & 4 (signal). Click here to check thermistor values. Click here to check thermistor procedures. |
Sr & Audible Alarm | Fault with control board. | Check LP gas solinoid valve wire connections at main control and valve. Click here to check P1 terminals 7 (12VDC) & 10 (gnd). Disconnect the main power to the control board, wait 30 seconds, re-power up to see if error is gone? If one has the Fridge Defend, just do the post install test with the SetUp button to turn off power to fridge. Click here to check all main board P1 terminals for proper signals, power & grounds. |
Thermistor Tables
The following value are approximate, there is error in test leads and other factors. Be sure to check all connections, the connections in the fridge can rust. We do not recomend using an ice bath, the water can get into the thermistor.
5'7 In Cm
TEMPERATURE (°F) | RESISTANCE (kΩ) |
---|---|
85 | 8.1 - 9.0 |
80 | 9.1 - 10.0 |
75 | 10.1 - 11.0 |
70 | 11.1 - 12.0 |
60 | 12.1 - 13.0 |
50 | 15.5 - 16.5 |
40 | 22.5 - 23.5 |
35 | 24.5 - 25.5 |
33 | 28.5 - 29.5 |
32 | 30.0 - 32.0 |