Form 8938 serves a different purpose than FBAR. The purpose of Form 8938 is to facilitate compliance with FATCA and is part of the tax return, while the FBAR was designed to aid in law enforcement. FBARs can be and are shared among governmental agencies and are used primarily by the Treasury Department's Financial Crimes Enforcement Network to track and combat international money laundering. People often get nervous when 'double-counting' money on FBAR when funds have been transferred between accounts, when there should generally not be such concern since it's not a taxation reporting. Form 8938 is designed to be used by the Internal Revenue Service for combating international tax evasion.
Taxpayers who have a requirement to file Form 8938 probably also have an obligation to report substantially the same information on the FBAR, which is filed separately with the Treasury Department.
The law states the following for Form 8938 (26 CFR 1.6038D-4 and 26 CFR 1.1471-5(b)(3))
Definition of deposit account - (1) A commercial, checking, savings, time, or thrift account, or an account that is evidenced by a certificate of deposit, thrift certificate, investment certificate, passbook, certificate of indebtedness, or any other instrument for placing money in the custody of an entity engaged in a banking or similar business for which such institution is obligated to give credit (regardless of whether such instrument is interest bearing or non-interest bearing), including, for example, a credit balance with respect to a credit card account issued by a credit card company that is engaged in a banking or similar business; or
(2) Any amount held by an insurance company under a guaranteed investment contract or under a similar agreement to pay or credit interest thereon or to return the amount held.
Definition of Custodial account - The term custodial account means an arrangement for holding a financial instrument, contract, or investment (including, but not limited to, a share of stock in a corporation, a note, bond, debenture, or other evidence of indebtedness, a currency or commodity transaction, a credit default swap, a swap based upon a nonfinancial index, a notional principal contract as defined in § 1.446-3(c), an insurance or annuity contract, and any option or other derivative instrument) for the benefit of another person.
The law states that for Form 114 (31 CFR 1010.350)
Bank account is - The term “bank account” means a savings deposit, demand deposit, checking, or any other account maintained with a person engaged in the business of banking.
Securities account is - The term “securities account” means an account with a person engaged in the business of buying, selling, holding or trading stock or other securities.
Other financial account is - The term “other financial account” means -
(i) An account with a person that is in the business of accepting deposits as a financial agency;
(ii) An account that is an insurance or annuity policy with a cash value;
(iii) An account with a person that acts as a broker or dealer for futures or options transactions in any commodity on or subject to the rules of a commodity exchange or association; or
(iv) An account with -
(A)Mutual fund or similar pooled fund. A mutual fund or similar pooled fund which issues shares available to the general public that have a regular net asset value determination and regular redemptions; or
(B)Other investment fund. [Reserved]
As a result of the above definitions it may be possible to have an account that should be classified as "Other" on Form 114 and also be a reportable account for Form 8938. Note that the way some tax prep software is set up, it is not possible to report an account as "other" for Form 114 and show it on Form 8938.
Similarly a securities account for Form 114, (an account held with a person engaged in buying and selling securities) could be a deposit account for Form 8938.