Should you use an ABN when transporting a patient?

I was trolling through CMS's FAQ Web page and found these four situations where Medicare's Advanced Beneficiary Notice (ABN) should or should not be used when transporting a patient.  Two of these situations show an ABN is applicable, according to CMS. However, an ABN cannot be used if it's an emergency transport because the patient is under durress.

1. Other means of transportation not contraindicated (meaning, increasing risk)
   ABN Applicable: No
   Limitation on Liability Applicable: No
   Responsible for Payment: the patient
2. Air to Ground Downcoding
   ABN Applicable: Yes
   Limitation on Liability Applicable: Yes
   Responsible for Payment: the supplier/provider or patient if ABN is signed
3. ALS to BLS Downcoding
   ABN Applicable: Yes
   Limitation on Liability Applicable: Yes
   Responsible for Payment: the supplier/provider or patient if ABN is signed
4. Mileage Partial Denial
   ABN Applicable: No
   Limitation on Liability Applicable: No
   Responsible for Payment: the patient