Under what circumstances can angels manifest in human form? Is that common in carrying out rescues to prevent untimely death of humans?

This is actually quite common. It is often the case that a physical agent is required to create a divine intervention that happens without appearing to be supernatural, which is in keeping with the rules of engagement, to not create an impressive divine display that will compel people to believe and will interfere with free choice. Part of the challenge of the current life experience for humanity is that of maintaining faith under conditions of a quite severe disconnection from the Divine, and awareness of the divine realm, and existence of Creator as a certainty. Few have anything close to an ongoing communion with Creator, so they know with certainty that the Almighty is very much a real presence continually for everyone. The doubt present among all humans a considerable percentage of the time, is an extreme test of faith and is one of the paradoxical advantages of the exercise in play. There is nothing like an acid test to temper one’s experience and learning through challenge and adversity that toughens an individual and forces them to grow new muscles to cope better or even survive. There will be seen in the future, by all, the great benefit to the exercise all are undergoing in coming from behind, having a tenuous link to the divine realm to sustain faith, and to be in so diminished a form, and subject to the frailties and suffering of physical human existence, where there are so many ways to become impaired or to die before one’s time—and so few certainties to guide human conduct towards what is truly highest and best, with so many voices, so many perspectives, so many sources of corruption to second-guess and question, and conflict with cherished notions of the past. There are many trials and tribulations that test the resolve, and the resiliency, and inner strength, and the character of all taking part. The angelics help preserve the link, and support people with all they do, and can be a source of direct inspiration and healing assistance many times during the course of life and are a great blessing because of the extreme challenges facing human.