What requirements are there to fly into KDCA?
The &quot;special notices&quot; are a section of the A/FD, but those notices paint a very incomplete picture. Both the FAA and the TSA have requirements regarding DCA. The very basics are that you must get authorization from both the FAA and TSA 24 hours in advance, you must have an armed security officer, and you must depart from a gateway airport.
The details are, well...
FAA Requirements

Regulations require an arrival/departure slot to be reserved via the e-CVRS system during most hours, just like other airports designated as high-density airports.
Flights to DCA must originate from within a 1250 mile perimeter (with limited exceptions).


TSA requirements
The TSA requirements are referred to as the DCA Access Standard Security Program (DASSP). An overview is given on this tsa.gov page (scroll down to &quot;DCA Access Standard Security Program&quot;).
Details can be found in the Interim Final Rule... because calling the ruling both interim and final won't confuse anyone. Here is a summarization of that document:
Section A. Aircraft Operator Requirements:

Security Coordinators The aircraft operator (company) must have a designated security coordinator who is the point of contact for the TSA and is responsible for implementing the DASSP requirements. This person must undergo a TSA security threat assessment, and a fingerprint-based criminal history records check (CHRC) by the FBI.

DCA Access Standard Security Program (DASSP) TSA will verify the operator's status with the FAA before sending the DASSP document which contains &quot;sensitive security information&quot; which must be implemented, and the operator must notify TSA when all requirements have been implemented.

Flightcrew Members Each flight crew member (does not include flight attendants) must undergo a fingerprint-based CHRC and an FAA record check. Almost any prior restricted airspace violation is an immediate disqualifier.

Flight Approvals Each flight into or out of DCA requires a tentative slot reservation from the FAA (see FAA reqirement #1 above) before applying for TSA authorization. The TSA application must be submitted at least 24 hours prior to aircraft departure. If TSA approves the application, they will transmit this to the FAA which will issue the final slot reservation, and TSA will notify the operator. The TSA only approves up to 48 applications for a given date. The application must include (once per round-trip):

The name, address, and citizen status of each passenger and crewmember (includes flight attendants).
The registration number of the aircraft.
The flight plan.
and... &quot;any other information required by TSA.&quot;


Operating Requirements Each flight must:

be operated under instrument flight rules.
not make any intermediate stops between the designated gateway airport and DCA.
have the aircraft, crew, passengers, and property inspected by TSA prior to departure.
have the cockpit door closed and locked for the duration of the flight (if equipped).
have at least one armed security officer who meets the armed security officer requirements.


Costs TSA charges \$15 for each crew member and passenger to conduct the security threat assessment. Additionally, they charge for the screening services at the airport which are &quot;currently estimated at \$296 per round trip into and out of DCA.&quot;

Protection of Sensitive Security Infonnation The specific security details described in the DASSP must only be shared on a need-to-know basis.

Other Security Procedures This paragraph basically says TSA can make you do whatever they want... as if that wasn't obvious by this point in the list.

Compliance TSA can perform any inspection or test it wants to verify the operators compliance with DASSP.


Section B. Fixed Base Operator Requirements
That's right, there are two section B's, one right after the other... in case you weren't already convinced the TSA has strong attention to detail.
This section just says there are FBO requirements for gateway airports. Here is a list of Gateway Airports dated March 21, 2013. The list is always subject to change and seems to have more to do with whether there is an FBO at the airport who wants to put up the DASSP more than anything else.
Section C. Armed Security Officer Requirements
Armed security officers must be an active or retired law enforcement officer, or an individual approved by the TSA. This requires a similar background check as the security coordinator and law enforcement training which TSA finds acceptable. For more information, see the Armed Security Officer (ASO) Program.
Flying under Part 91?
At first glance it doesn't seem like there is any rule explicitly prohibiting Part 91 operations in 49 CFR Part 1544, and §1544.1 Applicability of this part. says:

(a) This part prescribes aviation security rules governing the following:
(1) The operations of aircraft operators holding operating certificates under 14 CFR part 119 for scheduled passenger operations, public charter passenger operations, private charter passenger operations; the operations of aircraft operators holding operating certificates under 14 CFR part 119 operating aircraft with a maximum certificated takeoff weight of 12,500 pounds or more; and other aircraft operators adopting and obtaining approval of an aircraft operator security program.

The general definition of an aircraft operator is not limited to an operator with a Part 119 operating certificate. However, the possibility of using part 91 seems to be ruled out by §1544.101 Adoption and implementation. where it enumerates the scenarios TSA is willing to approve, and there are no Part 91 operations in the list.
There are probably a few reasons why Part 91 is not allowed. Most notably:

TSA has specific aircraft operator requirements which an individual operator is unlikely to be able to comply with, and
There are only 48 slots available per day, and therefore preference is given to commercial operators - the explicitly given explanation for why non-airline flights are permitted at all is to permit &quot;operators, their customers, and affected local businesses to recover from the adverse economic impacts brought on by the events of September 11, 2001.&quot;

Other fun quotes:

TSA may, at its discretion, require any flight into or out of DCA under this subpart to comply with additional security measures.

and...

In addition, if TSA or the FAMS requires that the aircraft have one or more Federal Air Marshals (FAMs) on board, the aircraft operator must allow the FAM(s) onboard, at no cost to the Federal Government.

and...

TSA may, at its discretion, cancel any or all flight approvals at any time without prior notice to the aircraft operator. For example, if the threat level in the Washington, D.C., area or in the vicinity of any of the gateway airports is set at ORANGE or RED, TSA is likely to cancel any and all flight approvals into and out of DCA.

So, happy flying everyone!