I believe that this is the only FBO left at Logan, an airport that hates GA more than any other public North American airport (thanks to Massport). I called Signature just to see how bad the fees are, and here's what I got for a two-night stay in a Piper Cherokee (note that not all of them are under Signature's control):
$33.00 landing fee
$166.60 parking (2 nights)
$48.40 GA fee (!!)
$56.00 security fee
$28.00 handling fee (waived with 7 gallons fuel purchase)
I didn't ask about a customs fee, but there's a steep one at Bedford/Hanscom (also run by Massport), so I expect there's one here as well. I think the security fee is for being poked, prodded, and metal-detected by the TSA, just like if you were flying on the airlines.
By comparison, if I flew my Cherokee into Washington/Dulles (another large airport affected by 9/11) and parked at the Signature there, I'd pay an $8.00 landing fee, $18.19/night parking, no customs fee, no security fee, no GA fee, and the same $28.00 handling fee (waived with 7 gallon fuel purchase).
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