How aggressively one should pursue SSDI concurrently as one is preparing, formulating and filing for Federal Disability Retirement benefits from the U.S. Office of Personnel Management, is a question which one is often confronted with during the process of filing for Federal Disability Retirement benefits.
If one is under CSRS, then the question is a moot point, because CSRS employees do not have a requirement of filing for SSDI benefits.
For FERS employees, however, who make up the vast majority of Federal and Postal employees who file for Federal Disability Retirement benefits from the U.S. Office of Personnel Management, there is a requirement of filing concurrently for Social Security Disability Insurance (SSDI) benefits. For purposes of satisfying the requirement of OPM, one needs to only show a receipt that one has filed. Further, while many Human Resources personnel offices, both for Federal agencies and the U.S. Postal Service (the latter being comprised of the central office known as the H.R. Shared Services Center located in Greensboro, N.C.), misinform and misinterpret the statutory requirement of filing for SSDI, by telling people either that one must file and get a decision from the Social Security Administration prior to filing for FERS Disability Retirement benefits (wrong), or that you cannot file for FERS Disability Retirement unless and until you file for SSDI (also wrong) — the fact is, the only time OPM requires a showing of having filed for SSDI is at the time of an approval of a FERS Disability Retirement application.
As for how actively or aggressively one should pursue SSDI? That depends, in most cases, on whether you will be attempting to work in a private sector job while on Federal Disability Retirement. Because SSDI has stringent limits on what you can make in earned income, while OPM Disability Retirement allows for you to make up to 80% of what your former position currently pays, on top of the disability retirement annuity one receives, it becomes a pragmatic calculation.
Pragmatism is the guiding light to determine one’s self-interest, and that which is in the best interest of one’s future.
Sincerely,
Robert R. McGill, Esquire
OPM Disability Retirement 
Why does both federal agencies blame each another (owcp,opm) when an claimant elects workers comp over disability retirement and the agency delays retroactive pay to claimant because the agency will not pay claimant before the agency pays the other agency an overpayment first. Yet both agencies refuses to follow one’s protocol. Its been six month’s and waiting.