Trauma codes transported by helicopter have a less than 1 percent survival rate in the US. There has been some talk of changing the protocol to not fly a trauma patient without a pulse due to the risks to the air crew. It’s a higher chance of the helicopter crashing than the odds of the patient making it out of the hospital.
For trauma patients, there’s a 39% lower death rate for HEMS vs ambulance transportation, according to one study:
https://pubmed.ncbi.nlm.nih.gov/21524205/
[The odds of death were 39% lower in those transported by HEMS compared with those transported by ground ambulance (AOR = 0.61, 95% confidence interval [CI] = 0.54-0.69). Among those aged ≥ 55 years, the odds of death were not significantly different (AOR = 0.92, 95% CI = 0.74-1.13). Among all transports, male patients had a higher odds of death (AOR = 1.23, 95% CI = 1.10-1.38) than female patients. The odds of death increased with each year of age (AOR = 1.040, 95% CI = 1.037-1.043) and each unit of ISS (AOR = 1.080, 95% CI = 1.075-1.084), and decreased with each unit of RTS (AOR = 0.46, 95% CI = 0.45-0.48). ]