MTBF Calculation and MTBF Analysis Frequently Asked Questions (FAQ).
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Instant MTBF Report Frequently Asked Questions

Q: Will the Reliability MTBF Prediction Report that I purchase from your website satisfy my requirement for an MTBF?

A: Yes!  We have been producing Reliability Prediction Reports for over 35 years.  Our clients are companies that must qualify their equipment to Commercial, DOD, DOE, DOT, FAA, NASA, NRC or FDA requirements.  Click the links above to review our Clients and Projects.

Our Instant MTBF Reports incorporate the Parts Count methods for failure rate assignment as defined in MIL-HDBK-217F, Bellcore TR-332 and Telcordia SR-332.  These data sources provide the most widely accepted failure rate data and are the industry standards for reliability MTBF predictions.  These standards are well known by experts in the reliability engineering field. 

Our reports are conservative.  The Parts Count methods defined in MIL-HDBK-217F, Bellcore TR-332 and Telcordia SR-332 assume an electrical stress ratio of 50%.  The mathematical model reflects the reliability series model only.  If your equipment contains redundancy and you are looking for the best possible MTBF value, we can incorporate the redundant model into the report for an additional charge.  However, for most MTBF requirements, the conservative series model will suffice.

Q: What is an “Instant Reliability MTBF Prediction Report”?

A: An "Instant Reliability MTBF Prediction Report" is the Mean Time Between Failure (MTBF) of your equipment delivered instantly in a Reliability Prediction Report.  The report is prepared in accordance with MIL-HDBK-217F (N1/2), Appendix A, Parts Count Method, the Commercial/Bellcore TR-332 Parts Count Method I or the Commercial/Telcordia SR-332 Parts Count Method I.  Your choice.  All you need to do is enter quantities of each part type used in your equipment.  It's that simple.  We process your data, enter it into a Reliability Prediction Report, and e-mail it to you within minutes. 

The report you will receive is a complete Reliability Prediction Report that includes a title page, table of contents, introduction and summary, resulting MTBF value, reliability and MTBF mathematical models for a series (non-redundant) system, environment and parts quality level description, and a MIL-HDBK-217F (N1/2) or Commercial/Bellcore TR-332 or Commercial/Telcordia SR-332 Parts Count Prediction Method description. The Reliability Prediction Report also contains an Appendix which presents the "Parts Failure Rate Data" tabulations that support the MTBF calculation. 

Q: What is the quickest and least expensive way I can get a Reliability MTBF Prediction Report?

A: Begin by visiting our “Instant MTBF” web page.  Click on the link that reads “Print blank Data Input Screen to paper”.  Give the data input sheets to an engineer and ask him to write down the quantities of each part type in your equipment.  (Note: If you want your report to reflect the system breakdown by assembly, have the engineer fill out one set of Data Input Sheets for each assembly in your system).

Once the data input sheets are filled in, visit our “Instant MTBF” web page. Click the link “Click Here to access the Data Input Screen...” to begin entering the parts quantities into the computer.  There are 4 steps to complete this process: 

  1. Enter the user contact information
  2. Enter the parts quantities
  3. Confirm that the data has been entered correctly by clicking the Approved button
  4. Enter your credit card payment information

Once the above steps are completed, the Reliability MTBF Prediction Report should arrive in your e-mail within 10 to 15 minutes.

Q: What if I can’t find one of my parts listed on your Data Input Sheets?

A: Three suggestions:  1.  Enter the part as a “special part” in the space provided at the bottom of the Data Input Sheet.  2.  Enter part quantities adjacent to a part on the data input sheet that is most similar to your part.  3.  Send us your parts list or bill of materials (BOM) and we will enter the quantities for you.  For this service we charge $1,500.00, assign an experienced engineer to perform the analysis and prepare the report, and we offer a delivery schedule of 24 to 48 hours.

Q: What Environment should I use for the Reliability MTBF Prediction Report?

A: You will need to select one environment from the following table.  The Environment Description, Part Ambient Temperature and Semiconductor Junction Temperature may help you choose the environment that is appropriate for your equipment.

MIL-HDBK-217F(N1/2) or Commercial/Bellcore TR-332 Environments 

Abb. Environment Description Part Ambient
Temp. ~ ºC.
 
Semiconductor
Junction Temp.
~ ºC.
GB Ground, Benign

30

50

GF Ground, Fixed

40

60

GM Ground, Mobile

45

65

NS Naval, Sheltered

40

60

NU Naval, Unsheltered

45

65

AIC Airborne, Inhabited Cargo

55

75

AIF Airborne, Inhabited Fighter

55

75

AUC Airborne, Uninhabited Cargo

70

90

AUF Airborne, Uninhabited Fighter

70

90

ARW Airborne, Rotary Winged

55

75

SF Space, Flight

30

50

MF Missile, Flight

45

65

ML Missile, Launch

55

75

CL Cannon, Launch

40

60

Commercial/Telccordia SR-332 Environments

Abb. Environment Description
GB Ground, Fixed, Controlled
GF Ground, Fixed, Uncontrolled
GM Ground, Mobile (Both Vehicular Mounted and Portable)
AC Airborne, Commercial
SC Spacebased, Commercial


Q: What if the Part Ambient Temperature in the table above does not match my requirement?

A: MIL-HDBK-338B, Paragraph 10.3.1.1, “Reliability Adjustment Factors” contains Table 10.3-4 presented below.  The MTBF presented in the MIL-HDBK-217F(N1/2) or Commercial/Bellcore TR-332 Reliability Prediction Report can be adjusted using the table below. 

TABLE 10.3-4:  TEMPERATURE CONVERSION FACTORS

(MULTIPLY SERIES MTBF BY)

To Temperature (°C)

From Temperature (°C)

Temp.

10

20

30

40

50

60

70

10

X

0.9

0.8

0.8

0.7

0.5

0.4

20

1.1

X

0.9

0.8

0.7

0.6

0.5

30

1.2

1.1

X

0.9

0.8

0.6

0.5

40

1.3

1.2

1.1

X

0.9

0.7

0.6

50

1.5

1.4

1.2

1.1

X

0.8

0.7

60

1.9

1.7

1.6

1.5

1.2

X

0.8

70

2.4

2.2

1.9

1.8

1.5

1.2

X

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